Metrohm 757 VA Computrace Hardware Manual

757 VA Computrace

METROHM Ltd.
CH-9101 Herisau

Hardware Manual

8.757.1013

CH-9101 Herisau/Schweiz
Internet www.metrohm.com
E-Mail [e-mail]

757 VA Computrace

Hardware Manual

8.757.1013

14.09.2001 / dö

Table of contents

757 VA Computrace – Hardware

I

Table of contents

1 Introduction

.........................................................................................

1

1.1 Instrument description......................................................................1

1.2 Information about the Instructions for Use....................................2

1.2.1 Organization ...........................................................................2

1.2.2 Notation and pictograms........................................................ 3

1.3 Support documentation ....................................................................4

1.3.1 Application Bulletins ...............................................................4

1.3.2 Application Notes ...................................................................6

1.3.3 Monographs ...........................................................................6

1.3.4 Reprints................................................................................... 6

2 Parts and controls

.........................................................................

7

3 Installation

.........................................................................................

13

3.1 Setting up the instrument............................................................... 13

3.1.1 Packaging.............................................................................13

3.1.2 Check.................................................................................... 13

3.1.3 Location ................................................................................13

3.2 Installation of the 757 VA Computrace Stand..............................14

3.2.1 Mains cable and mains connection...................................... 14

3.2.2 Switching the instrument on/off ............................................14

3.2.3 Connection to the PC ...........................................................15

3.2.4 Equipping the measuring head ............................................16

3.2.5 Inert gas connection ............................................................. 19

3.3 Multi-mode electrode (MME)...........................................................21

3.3.1 Construction and operating characteristics of the MME ......21

3.3.2 Filling the MME with mercury................................................ 23

3.3.3 Mounting the capillary ..........................................................24

3.3.4 Filling the capillary without vacuum...................................... 24

3.3.5 Filling the capillary using vacuum......................................... 26

3.3.6 Storing the MME ...................................................................30

3.3.7 Replenishing the mercury (without changing capillary)........ 30

3.3.8 Changing the capillary.......................................................... 31

3.3.9 Cleaning the MME ................................................................ 32

3.4 Rotating disk electrode (RDE)........................................................34

3.4.1 Construction and startup of the RDE.................................... 34

3.4.2 Regenerating the RDE .......................................................... 34

3.5 Reference electrode.........................................................................36

3.5.1 Construction .........................................................................36

3.5.2 Startup procedure................................................................. 37

3.6 Auxiliary electrode...........................................................................38

3.6.1 Construction .........................................................................38

3.6.2 Startup procedure................................................................. 38

3.7 Stirrer .................................................................................................39

3.8 Connection of 765 Dosimats .......................................................... 40

3.8.1 Electrical connection and setup ...........................................40

3.8.2 Tubing connection ................................................................ 40

3.8.3 Changing the Exchange unit ................................................41

Table of contents

757 VA Computrace – Hardware

II

3.9 Connection of the 813 Compact Autosampler............................ 43

3.9.1 Electrical connection ............................................................ 43

3.9.2 Tubing connections.............................................................. 46

3.9.3 Software settings.................................................................. 48

3.9.4 Operation of the 813 Compact Autosampler ....................... 50

4 Safety

......................................................................................................

51

4.1 Electrical safety................................................................................ 51

4.2 Safety considerations concerning mercury ................................ 52

4.2.1 Properties of mercury ........................................................... 52

4.2.2 Toxicity of mercury and its compounds ............................... 53

4.2.3 Handling of mercury............................................................. 53

4.2.4 References dealing with mercury ......................................... 55

5 Technical data

...............................................................................

57

6 Appendix

..............................................................................................

61

6.1 Scope of delivery............................................................................. 61

6.1.1 2.757.0110 VA Computrace ................................................. 61

6.1.2 2.757.0120 VA Computrace ................................................. 66

6.2

Options.............................................................................................. 68

6.3 Warranty............................................................................................ 71

6.4 EU Declaration of conformity......................................................... 72

6.5 Certificate of conformity and system validation......................... 73

6.6 Index .................................................................................................. 74

List of figures

Fig. 1: Front of the 757 VA Computrace Stand .................................................. 8

Fig. 2

: Rear of the 757 VA Computrace Stand................................................... 9

Fig. 3

: Right side view of the 757 VA Computrace Stand ................................ 10

Fig. 4

: Left side view of the 757 VA Computrace Stand................................... 10

Fig. 5

: Connection to PC .................................................................................. 15

Fig. 6

: Measuring head arm ............................................................................. 17

Fig. 7

: Scheme showing the inert gas connections ......................................... 20

Fig. 8

: Multi-mode electrode ............................................................................ 22

Fig. 9

: Adding the mercury............................................................................... 23

Fig. 10

: Setting up the filling station................................................................... 27

Fig. 11

: Filling the capillary................................................................................. 27

Fig. 12

: Measuring head arm with rotating disk electrode (RDE) ...................... 35

Fig. 13

: Construction of the reference electrode................................................ 36

Fig. 14

: Construction of the auxiliary electrode.................................................. 39

Fig. 15

: Electrical connection of the 813 Compact Autosampler....................... 44

Fig. 16

: Tubing connections for operation of the 813 Compact Autosampler... 44

Fig. 17

: Installation of accessories for rinsing and siphoning off....................... 45

Fig. 18

: Adjusting the pipetting needle .............................................................. 46

1.1 Instrument description

757 VA Computrace – Hardware

1

1 Introduction

1.1 Instrument description

757 VA Computrace is a PC-controlled system for voltammetry, which consists of
the following parts:

1.757.0010

VA Computrace Stand

with accessories

6.5326.000

VA Computrace Interface

6.2135.010

Connecting Cable

6.6032.100

VA Computrace Software 2.0

For a detailed description of the PC software «VA Computrace 2.0» see the

757

Software Manual

.

This

757 Hardware Manual

describes the installation and maintenance of the 757
VA Computrace Stand and its accessories. The central element of this Stand is the
multi-mode electrode (MME), which combines the dropping mercury electrode
(DME/SMDE) and the stationary hanging mercury drop electrode (HMDE) in a sin­gle construction. The rotating disk electrode (RDE) can also be used in the stand.

The parameters necessary for the VA measurement are sent from the PC to the VA
Computrace Interface via USB connection. The data acquisition at the 757 VA
Computrace Stand is started and controlled by the VA Computrace Interface, which
receives and stores the measurement data. At the end of the determination, the re­corded data are sent back to the PC where they are evaluated and saved in a de­termination file.

Operation of the 757 VA Computrace Stand follows the potentiostatic 3-electrode
principle in which the voltage of the working electrode is controlled by means of a
virtually currentless reference electrode to the preset desired value and the current
flows across a separate auxiliary electrode.

1 Introduction

757 VA Computrace – Hardware

2

1.2 Information about the Instructions for Use

Please read through these Instructions for Use carefully before you put
the 757 VA Computrace Stand into operation. The Instructions for Use
contain information and warnings to which the user must pay attention
in order to assure safe operation of the instrument.

1.2.1 Organization

These

8.757.1013 Hardware Manual

for the 757 VA Computrace Stand provide a
comprehensive overview of the installation, operation, and technical specifications
of these instruments. The Instructions for Use are divided into the following 6 sec­tions:

Section 1 Introduction
Section 2 Parts and controls

Numbers and designations of the parts and controls

Section 3 Installation

Installation of 757 VA Computrace Stand
Installation of working, reference and auxiliary electrodes
Attachment of 765 Dosimats
Attachment of the 813 Compact Autosampler

Section 4 Safety

Electrical safety
Safety considerations in the handling of mercury

Section 5 Technical data
Section 6 Appendix

Scope of delivery, options, warranty, index

To find the required information on the instrument please use either the

Table of

contents

or the

Index

at the back.

1.2 Information about the Instructions for Use

757 VA Computrace – Hardware

3

1.2.2 Notation and pictograms

The following notations and pictograms (symbols) are used in these Instructions for
Use:

Mode

Parameter or entry value

15

Part or control of 757

Hazard

This symbol draws attention to a
possible danger to life or of injury if
the associated directions are not
followed correctly.

Warning

This symbol draws attention to
possible damage to instruments or
instrument parts if the associated
directions are not followed cor­rectly.

Caution

This symbol marks important
information. First read the associ­ated directions before you con­tinue.

Comment

This symbol marks additional
information and tips.

1 Introduction

757 VA Computrace – Hardware

4

1.3 Support documentation

1.3.1 Application Bulletins

The «Application Bulletin» is a collection of analytical methods, application exam­ples and literature references. Of Metrohm's approximately 200 Application Bulle­tins, ca. 60 refer to Polarography and Voltammetry. All these Application Bulletins
are available on request free of charge from your Metrohm supplier.

The examples listed here substantiate the versatility of the polarographic and volt­ammetric methods for a range of applications including both inorganic and organic
substances. At any time you will find an updated list of the Application Bulletins in
the Internet under « www.metrohm.com

».

No. Title

7 Literature dealing with the application of polarography for the analysis of petro-

leum and its derivates

21 Bibliography of polarographic determinations of lead in different materials

23 Some literature indications for the polarographic determination of organic nitro

compounds

36 Polarographic analysis – Half-wave potentials of inorganic substances

50 Polarographic determination of lead in petrochemical products

57 Polarographic determination of nicotine

60 Polarographic determination of fructose

70 Polarographic nitrate determination in water samples, soil and plant extracts,

vegetable juices, meat and sausage products, fertilizers, liquid manure etc.

73 Polarographic analysis – Half-wave potentials of organic substances

74 Polarographic and stripping voltammetric analysis methods for thallium, anti-

mony, bismuth and iron (copper, vanadium)

76 Polarographic determination of nitrilotriacetic acid (NTA) and ethylenediamine-

tetraacetic acid (EDTA)

96 Stripping voltammetric analysis of mercury

97 Voltammetric determination of tocopherols (vitamin E) in edible oils and fats

98 Determination of ascorbic acid (vitamin C) and its compounds

104 Polarographic analysis – Half-wave potentials of inorganic substances with

complexing agents in the background electrolytes

105 Determination of permissible lead and cadmium levels in crockery and glassware

108 Polarography – Conditions, limits of determination and half-wave potentials of 50

elements not yet listed in Application Bulletins Nos. 36, 73 and 104

110 Polarographic determination of free cyanide

113 Polarographic determination of lead, copper and tin present together in food-

stuffs, effluent waters, sewage sludges etc.

114 Polarographic determination of five metal ions (copper, cobalt, nickel, zinc and

iron) in a single operation

115 Bibliography concerning inverse voltammetry

116 Polarographic determination of chromium in small quantities

117 Determination of selenium by inverse voltammetry

1.3 Support documentation

757 VA Computrace – Hardware

5

No. Title

123 Voltammetric determination of iron and manganese in water samples

124 Polarographic analysis of metals – Half-wave potentials in an oxalate-buffer

background electrolyte

126 Polarographic determination of quinine

127 Polarographic determination of ammonium and nitrite

131 Voltammetric determination of aluminum

132 Polarographic determination of molybdenum in strongly ferruginous substances

and ferrous metals

136 Polarographic determination of styrene in polystyrenes and copolymers

141 Analysis of edible fats and oils

146 Direct polarographic determination of trace amounts of molybdenum in water

147 Simultaneous trace determination of seven metal ions in « electronic grade»

materials with the aid of stripping voltammetry

176 Simultaneous determination of lead and tin by anodic stripping voltammetry

179 Polarographic determination of maleic and fumaric acid alone or in mixtures

186 Adsorptive voltammetric determination of aluminum in water samples

190 Polarographic determination of 4-carboxybenzaldehyde in terephthalic acid

191 Polarographic determination of cystine and cysteine simultaneously

192 Polarographic and stripping voltammetric determination of thiourea in the lower

ppm and ppb range

196 Polarographic determination of formaldehyde

199 Polarographic determination of sulphide and sulphite

207 Stripping voltammetric analysis of silver

213 Polarographic determination of nicotinamide

215 Polarographic determination of folic acid (vitamin B9, vitamin BC)

218 Polarographic determination of thiamine (vitamin B1)

219 Polarographic determination of riboflavin (vitamin B2)

220 Determination of ultratrace levels of platinum by stripping voltammetry

221 Standard methods in water analysis – use of Metrohm instruments

224 Polarographic determination of pyridoxine (vitamin B6)

226 Determination of the total arsenic content by stripping voltammetry at the rotating

gold electrode

231 Voltammetric determination of zinc, cadmium, lead, copper, thallium, nickel and

cobalt in water samples according to DIN 38406 E 16

238 Check of Dosimats according to GLP/ISO

241 Determination of cadmium and lead at the « Ultra Trace» graphite electrode by

anodic stripping voltammetry

242 Determination of tungsten at the « Ultra Trace» graphite electrode by anodic

stripping voltammetry

243 Determination of chromium at the « Ultra Trace» graphite electrode by cathodic

stripping voltammetry

250 Polarographic determination of diazepam in body fluids and pharmaceutical

preparations

1 Introduction

757 VA Computrace – Hardware

6

No. Title

251 Polarographic determination of cinchocaine (dibucaine) in pharmaceutical

preparations

254 Determination of zinc, cadmium, lead and copper by anodic stripping voltam-

metry using carbon electrodes

266 Voltammetric determination of titanium and uranium

276 Validation of Metrohm VA instruments using Standard Operating Procedures

1.3.2 Application Notes

The «Application Notes» present application information in concentrated form. In
the field of voltammetry, there are at present approximately 120 Application Notes
(in English) which can be viewed in the Internet under « www.metrohm.com

» and

copied from there. All these Application Notes are printed in the

8.757.2003 VA

Applications Collection

supplied with the instrument.

1.3.3 Monographs

The «Metrohm Monographs» listed below impart theoretical fundamentals and
general information on measurement techniques and sample preparation of pola­rography and voltammetry. All these monographs are available on request free of
charge from your Metrohm supplier.

Title

First aid for polarography and voltammetry (8.693.1071)

Sample preparation techniques in voltammetric trace analysis

Inorganic Adsorptive Stripping Analysis

Organic Stripping Analysis

Stripping Voltammetry

Electrode Reaction Kinetics determined by Cyclic Voltammetry

The Application of VA Techniques to the Galvanic/Plating Industry

Practical voltammetry (8.757.5003)

1.3.4 Reprints

The following reprints reporting on practical applications are available on request
free of charge from your Metrohm supplier.

Title

Investigations of oxidative UV photolysis:
I. Sample preparation for the voltammetric determination of Zn, Cd, Pb, Cu, Ni and Co in
waters

Investigations of oxidative UV photolysis:
II. Sample preparation for the voltammetric determination of mercury in water samples

Determination of Zn, Cd, Pb, and Cu in soils and sewage sludges by microprocessor­controlled voltammetry in comparison with AAS

Voltammetric instrument for training and trace analysis

2 Parts and controls

757 VA Computrace – Hardware

7

2 Parts and controls

In this section you will find the numbers and designations of the parts
and controls of the 757 VA Computrace Stand. The numbering applies
throughout the instructions for use, i.e. bold numbers in the text (e.g.

15) refer to the parts and controls illustrated here.

2 Parts and controls

757 VA Computrace – Hardware

8

1

2

3

4

5

6

7

Fig. 1: Front of the 757 VA Computrace Stand

1

Cover of measuring head arm

hinged

5 Mains pilot lamp

lit up when instrument switched
on

2

Stopper (6.2709.080)

to close the pipetting opening

6 Measuring vessel

when measuring head arm is
fully raised, the measuring
vessel can be pulled forward out
of the holder 3

3

Holder for measuring vessel 7 Drip pan (6.2711.040)

4

Gas wash bottle (6.2405.030)

for inert gas supply (filling with
dist. water, see

section 3.2.5

)

2 Parts and controls

757 VA Computrace – Hardware

9

8

Type 1.757.0010 Nr.

f = 50-60Hz
P = 26W

Made by Metrohm Herisau Switzerland

PC InterfaceRemote

100-240V

STANDBY

ON

9

10

11

12

13

14

15

Fig. 2

: Rear of the 757 VA Computrace Stand

8

Connection for inert
gas lead-off

12 Mains switch (on/off)

on/off switching of instrument
(the pilot lamp 5 is lit up when
the instrument is on)

9

Connection for optional
waste solution lead-off

13

Mains connection plug

mains connection, see

section

3.2.1

10

Connection for inert gas
supply

required pressure:

p

= 1 ± 0.2 bar

14

Connection to VA Com­putrace Interface

connection socket for

6.2135.010 cable leading to the

6.2155.000 VA Computrace
Interface, see

section 3.2.3

11

Serial number

15 Connection

connection socket for 665/765
Dosimats and 813 Autosampler,
see

section 3.8

and

3.9

2 Parts and controls

757 VA Computrace – Hardware

10

16

17

2

18

19

20

21

22

23

24 25 22 26 27 28 4 29 30 26 31 32 33

Fig. 3

: Right side view of the 757 VA Computrace Stand (fully equipped)

50 49 48 47 46 31 28 42 39 25 41 40

17

2

39

19

20

3816373635

34

45 44 43

Fig. 4

: Left side view of the 757 VA Computrace Stand (fully equipped)

2 Parts and controls

757 VA Computrace – Hardware

11

2

Stopper (6.2709.080)

to close the pipetting opening

4 Gas wash bottle (6.2405.030)

for inert gas supply
(must be filled halfway with dist. H

2

O,

see

section 3.2.5)

16 Electrode cable ”WE”

connection for working electrode
(MME or RDE)

17 Multi-mode electrode (MME)

(6.1246.020)

details, see

section 3.3

18 FEP tubing (6.1805.180)

for inert gas supply to measuring vessel
(attached)

19 Measuring head arm

carrier plate with permanently attached
measuring head, raisable

20 Measuring head

measuring vessel upper half made of
PTFE; with openings for electrodes,
stirrer, gas and liquid supply lines

21 Dummy stopper (6.1446.040)

22 Reference electrode

comprising 6.0728.020 Ag/AgCl Refer­ence system and 6.1245.010 Electrolyte
vessel (details, see

section 3.5)

23 Nipple (6.2730.030)

for mounting the 4-way microtip 26 or a
dummy stopper

24 Drive shaft (6.1246.010)

holder for stirrer tip

42

25 PTFE tube (6.1819.000)

(attached)

26 4-way microtip (6.1824.000)

for delivery of solutions; with 4 lengths
of PTFE tubing with connecting nipples
for 765 Dosimat

27 Electrode cable ”RE”

connection for reference electrode

22

28 Drive belt (6.1244.020)

connection between drive wheel 31 and
drive shaft

24

29 PTFE tube (4.647.1350)

for inert gas delivery to gas wash bottle

4

(attached)

30 FEP tubing (6.1805.180)

for inert gas supply to MME

17

31 Drive wheel of drive motor

32 FEP tubing (6.1805.040)

for inert gas delivery to gas wash bottle

4

(attached)

33 Slotted screw for controlling the

inert gas flow

Note

: The factory setting of ca. 20 L/h

should not be changed without good
reason!

34 FEP tubing (6.1805.100)

for waste solution lead-off (attached)

35 FEP tubing (6.1805.090)

for inert gas lead-off (attached)

36 FEP tubing (6.1805.180)

for inert gas supply to tapping mecha­nism (attached)

37 Electrode cable ”AE”

connection for auxiliary electrode

39

38 FEP tubing (6.1805.180)

for inert gas supply to MME

17

39 Auxiliary electrode

details, see

section 3.6

40 Dummy stopper (6.1446.040)

41 Dummy stopper (6.1446.040)

2 Parts and controls

757 VA Computrace – Hardware

12

42 Stirrer tip (6.1204.090)

43 PTFE tube (6.1819.010)

for optional supply of the waste solution
to gas wash bottle 44 (attached)

44 Gas wash bottle (6.2405.030)

for separating mercury from the waste
solution (attached)

45 PTFE tube (6.1819.010)

for optional siphoning off the waste
solution from gas wash bottle 44
(attached)

46 Dummy cell connection ”WE-D”

differential mode simulation
(peak/wave)

47 Dummy cell connection ”WE-L”

linear mode simulation (RC element)

48 Dummy cell connection ”RE”

49 Dummy cell connection ”AE”

50 Slotted screw for controlling the

tapping power in the DME case

Note

: The factory setting should not be

changed without good reason!

3.1 Setting up the instrument

757 VA Computrace – Hardware

13

3 Installation

This section offers a full description of the 757 VA Computrace Stand
and provides detailed information on the various electrodes and the
stirrer. Reliable operation of the instrument is assured only if you follow
the instructions in this section exactly.

3.1 Setting up the instrument

3.1.1 Packaging

The 757 VA Computrace Stand is supplied together with the separately packed ac­cessories in special packages designed to ensure excellent protection. These con­tain shock-absorbing foam linings foamed to the individual shape and embedded in
blue plastic film. The instrument itself is packed in an evacuated polyethylene bag.
As only these special packaging guarantees indemnified transport of the instru­ment, it is essential you store it in a safe place.

3.1.2 Check

After receipt, immediately check whether the shipment is complete and has arrived
without damage (compare with delivery note and list of accessories in

sections 6.1

).

In the case of transport damage, see instructions in

section 6.3

"Warranty".

3.1.3 Location

Place the 757 VA Computrace on a laboratory bench in a position suitable for op­eration and which is free from vibrations, protected against corrosive atmospheres
and contamination by chemicals. The drip pan 7 (6.2711.040) has to be placed at
the front side of the 757 VA Computrace Stand to catch drops (see

Fig. 1

).

3 Installation

757 VA Computrace – Hardware

14

3.2 Installation of the 757 VA Computrace Stand

If the 757 VA Computrace Stand is connected to the power supply,
the instrument may not be opened or parts removed as there is a
danger of contact with live components. Before you open the 757 VA
Computrace Stand to change components or for maintenance or
repair work, always switch on the instrument by setting the mains
switch

12

to the ON position and then disconnect the mains cable

from the mains connection plug

13

of the 757 VA Computrace Stand !

3.2.1 Mains cable and mains connection

The instrument is supplied with one of three mains cables:

•

6.2122.020 with plug SEV 12 (Switzerland, …)

•

6.2122.040 with plug CEE(7), VII (Germany, …)

•

6.2133.070 with plug NEMA 5-15 (USA, …)

which are three-cored and fitted with a plug with an earthing pin. If a different plug
has to be fitted, the yellow/green lead (IEC standard) must be connected to protec­tive earth (protection class 1).

Any break in the earthing inside or outside the instrument can make it
a hazard!

Plug the mains cable into mains connection plug 13 of the 757 VA Computrace
Stand (see

Fig. 2

).

3.2.2 Switching the instrument on/off

The 757 VA Computrace Stand is switched on and off using mains switch 12. When
the instrument is switched on, the pilot lamp 5 lights up.

3.2 Installation of the 757 VA Computrace Stand

757 VA Computrace – Hardware

15

3.2.3 Connection to the PC

The 757 VA Computrace Stand is connected to the PC via 6.2155.000 VA Com­putrace Interface. Proceed as follows:

1 Software installation

•

Switch on PC and start operating system (Windows™

2000) without

connection of the VA Computrace Interface via USB cable.

•

Insert installation CD into CD drive.

•

If the autorun option for the CD drive is disabled, select

<Start>

and

Run

.

Browse for the

Setup.exe

file on the installation CD and click on

<OK>

.

•

Click on "

757

" and follow the instructions given in the setup program.

Select the

VA Computrace Interface (USB)

option for the interface type. The
software package will be installed in the desired directory (the default di­rectory is

Programs/Metrohm/757 VA Computrace

).

•

Restart the PC.

2 Connection of the VA Computrace Interface

•

Connect 6.2155.000 VA Computrace Interface to connection 14 "PC
Interface" of the 757 VA Computrace using the

6.2135.010 cable

and

switch on 757 VA Computrace Stand (see

Fig. 5

).

•

Connect VA Computrace Interface to the

6.2158.000 Mains Adapter

connected to the mains.

•

Connect VA Computrace Interface to the PC using the

6.2151.020 USB

cable

. The PC detects a new USB device and starts the setup wizard.
Insert installation CD into CD drive and follow the wizard instructions al­ways selecting the recommended default options.

•

Start the VA Computrace software.

757

6.2155.000 VA Computrace Interface6.2151.020 USB Cable

6.2135.010 Cable6.2158.000 Mains Adapter

PC

Mains

Fig. 5

: Connection to the PC

3 Installation

757 VA Computrace – Hardware

16

3.2.4 Equipping the measuring head

The fixtures inserted in the openings and connections of the measuring head 20 in
the 757 VA Computrace Stand depend on the working electrode selected (MME or
DME) (see

Fig. 6

). The fully equipped measuring head for operation with a multi-

mode electrode is illustrated in

section 2 (Figs 3 and 4

), that for operation with a ro-

tating disk electrode in

section 3.4 (Fig. 12

).

When equipping the measuring head for the first time, the best procedure is as fol­lows:

1 Preparations

•

Prepare multi-mode electrode MME 17 (details, see

section 3.3

) or rotat-

ing disk electrode RDE (details, see

section 3.4

) for operation.

•

Prepare reference electrode 22 (details, see

section 3.5

) for operation.

•

Tilt back cover 1 of measuring head arm.

2 Insert dummy stoppers

•

Screw dummy stopper 41 (6.1446.040) into opening 52.

•

Screw dummy stopper 40 (6.1446.040) into opening 53.

3 Insert 4-way microtip (option)

The 6.1824.000 4-way microtip has to be installed if 765 Dosimats are used
for automatic solution addition. Proceed as follows:

•

Remove stopper from nipple 23 and insert 4-way microtip

26

into nipple

23

as far as it will go.

•

Tighten nipple 23 using a 6.2739.010 Wrench until the 4-way microtip 26
can no longer move.

•

Pull the 4 lengths of PTFE tubing of the 4-way microtip 26 in succession
from above through the opening 65 (connection of 665 or 765 Dosimat,
see

section 3.8

).

4 Install stirrer or RDE

in operation with MME:

•

Screw stirrer tip

42

to drive shaft

24

(see also

section 3.7

).

•

Insert stirrer in opening

60

as far as it will go.

•

Stretch drive belt 28 (6.1244.020) between drive wheel 31 and drive shaft

24

of the stirrer.

in operation with RDE (option):

•

Screw electrode tip 99 (6.1204.XXX) to drive shaft

100

(6.1246.000)

(see also

section 3.4

).

•

Insert RDE in opening 60 as far as it will go.

•

Stretch drive belt 28 (6.1244.020) between drive wheel 31 and drive shaft

100

of the RDE.

•

Attach electrode cable 16 (WE) to the RDE: push cable lug under the
screw and then tighten screw firmly.

3.2 Installation of the 757 VA Computrace Stand

757 VA Computrace – Hardware

17

64595857 6261

51

52

53

54

55

656056 63

20

19

66 67

Fig. 6

: Measuring head arm

19 Measuring head arm
20 Measuring head
51 Opening

for auxiliary electrode 39 (6.0343.000 Pt
auxiliary electr. or optional GC electr.
comprising 6.1241.020 Electrode holder
and 6.1247.000 GC tip)

52 Threaded opening

for dummy stopper 41 (6.1446.040)

53 Threaded opening

for dummy stopper 40 (6.1446.040)

54 Pipetting opening

for the manual addition of solutions,
closed with stopper 2 (6.2709.080).

55 Opening

in operation with MME:

for multi-mode electrode 17
(6.1246.020)

in operation with RDE:

for 6.2709.040 Stopper (option)

56 Threaded opening

for FEP tubing 18 (6.1805.180, already
permanently attached); inert gas supply
to measuring vessel 6

57 Threaded opening

for dummy stopper 21 (6.1446.040)

58 Opening

for reference electrode 22 (6.0728.020
Ag/AgCl reference system and

6.1245.010 Electrolyte vessel)

59 Threaded opening

for nipple 23 (6.2730.030) with dummy
stopper or 4-way microtip 26
(6.1824.000)

60 Opening

in operation with MME:

for stirrer, comprising drive shaft 24
(6.1246.010) and stirrer tip 42
(6.1204.090)

in operation with RDE:

for rotating disk electrode (option),
comprising drive shaft

100

(6.1246.000)

and electrode tip 99 (6.1204.XXX)

61 Threaded opening

for FEP tubing 36 (6.1805.180, already
permanently attached); inert gas supply
for tapping mechanism

62 Threaded opening

for FEP tubing 35 (6.1805.090, already
perm. attached); inert gas lead-off

63 Threaded opening

for FEP tubing 18 (6.1805.180, already
permanently attached); inert gas supply
from gas wash bottle 4 to measuring
vessel 6

64 Threaded opening

for FEP tubing 32 (6.1805.040, already
permanently attached); inert gas supply
to gas wash bottle 4

65 Opening

for feedthrough of tubing connections of
4-way microtip 26 (6.1824.000)

3 Installation

757 VA Computrace – Hardware

18

66 Threaded opening

for FEP tubing 68 (6.1805.180); optional
waste solution lead-off

67 Threaded opening

for FEP tubing 34 (6.1805.090, already
permanently attached); optional waste
solution supply from gas wash bottle to
waste

5 Install reference electrode

•

Insert reference electrode

22

in opening 58.

•

Attach electrode cable 27 (RE) to reference electrode 22: push cable lug
under the screw and then tighten screw firmly.

•

Turn reference electrode 22 so that the electrode cable 27 points to the
rear and not to the side (in the latter position it may become kinked and
damaged when cover 1 is closed).

6 Install auxiliary electrode

•

Insert auxiliary electrode

39

(6.0343.000 Pt auxiliary electrode or GC

auxiliary electrode, see

section 3.6

) in opening 51.

•

Attach electrode cable 37) (AE) to auxiliary electrode 39: push cable lug
under the screw and then tighten screw firmly.

•

Turn auxiliary electrode 39 so that the electrode cable 37 points to the
rear and not to the side (in the latter position it may become kinked and
damaged when cover 1 is closed).

7 Install MME or dummy stopper

in operation with MME:

•

Carefully insert multi-mode electrode

17

(6.1246.020) in opening 55 (the
underside of the capillary must not touch the measuring head during in­sertion) and push in as far as it will go.

•

Screw FEP tubing 30 (6.1805.180) for inert gas supply into connection

72

of the MME 17.

•

Screw FEP tubing 38 (6.1805.180) for inert gas supply into connection

73

of the MME 17.

•

Attach electrode cable 16 (WE) to screw connection

89

of the MME 17:

push cable lug under the screw and then tighten screw firmly.

in operation with RDE (option):

•

Insert stopper 98 (6.2709.040, option) into opening 55 as far as it will go
so that the two blind holes point to the rear of the stand.

•

Screw FEP tubing 30 (6.1805.180) into upper hole of stopper 98.

•

Screw FEP tubing 38 (6.1805.180) into lower hole of stopper 98.

8 Install measuring vessel

•

Tilt back measuring head arm 19.

•

Slide measuring vessel 6 into holder 3 from the front and fill with analyte
solution or dist. H

2

O (storage solution) until the tips of the MME and the

reference electrode are immersed in the liquid.

•

Lower measuring head arm 19 and cover 1.

3.2 Installation of the 757 VA Computrace Stand

757 VA Computrace – Hardware

19

3.2.5 Inert gas connection

Nitrogen (N2) is generally used as the inert gas to deaerate the analyte solution and
for operation of the MME. The nitrogen must be of sufficient purity.

w

(N

2

) ≥ 0.99996 (= 99.996%)

for general polarography/voltammetry

w

(N

2

) ≥ 0.99999 (= 99.999% = "5 × 9")

for analyses in organic solvents; for determinations involving very
high current amplification (e.g. in the determination of very low con­centrations without preceding enrichment)

The scheme for deaeration of the analyte solution and the inert gas connections at
the 757 VA Computrace Stand needed for operation of the MME is shown in

Fig. 7

.

The inert gas connections are established as follows:

1 Fill gas wash bottle

•

Unscrew gas wash bottle 4 from measuring head arm 19.

•

Fill gas wash bottle 4 half full with dist. H

2

O (for long-term measurements

with supporting electrolytes such as HAc buffer or NH

3

buffer, fill with
supporting electrolyte; for measurements in organic solvents fill with the
used solvent).

•

Screw gas wash bottle 4 back on measuring head arm 19.

2 Connect inert gas supply

•

Attach one end of 6.1801.080 PVC tubing to connection

10

of the 757 VA

Computrace Stand.

•

Attach the other end of the 6.1801.080 PVC tubing to connection of the
inert gas bottle.

•

Set inert gas pressure at gas bottle using the reducing valve to

p

= 1 ± 0.2 bar.

•

Open gas supply line at gas bottle.

3 Connect inert gas lead-off (option)

•

Attach a length of suitable tubing (e.g. Metrohm 6.1805.030, length
150 cm) to connection 8 for inert gas lead-off.

•

Route the other end of the lead-off tubing to a fume cupboard.

3 Installation

757 VA Computrace – Hardware

20

N

2

V

3

V

2

V

4

V

1

4

33

50

72 73

Fig. 7

: Scheme showing the inert gas connections at the 757 VA Computrace Stand

4

Gas wash bottle (6.2405.030)

for inert gas supply (must be filled only halfway with dist. H

2

O or

supporting electrolyte, see also

Fig. 3

)

33

Slotted screw for controlling the inert gas flow for deaeration

(see also

Fig. 3

)

Note

: The factory setting of ca. 20 L/h should not be changed

without good reason!

50

Slotted screw for controlling the tapping power in the DME
case

(see also

Fig. 4

)

Note

: The factory setting should not be changed without good

reason!

72 Connection for inert gas supply of the MME

for raising and lowering the sealing needle in the MME (see also

section 3.3.1 and Fig. 8)

73 Connection for inert gas supply of the MME

for pressurizing the mercury (see also

section 3.3.1 and Fig. 8)

V

1…V4

Valves

3.3 Multi-mode electrode (MME)

757 VA Computrace – Hardware

21

3.3 Multi-mode electrode (MME)

The multi-mode electrode combines the most important polarographic and volt­ammetric mercury electrodes in a single construction:

• HMDE Hanging mercury drop electrode

Mercury is forced through a glass capillary until a drop
forms at the capillary tip and the entire voltage sweep
performed on this single stationary drop; in general
with preceding enrichment (stripping voltammetry).

• DME

Dropping mercury electrode

The classical electrode, the mercury drops fall from the
glass capillary at a controlled rate.

• SMDE Static mercury drop electrode

The latest electrode, it combines the features of the
DME and the HMDE: during the measurement, the
drop surface is constant and stationary (as with the
HMDE); however, for the complete voltage sweep sev­eral drops are needed (renewal as with the DME).

3.3.1 Construction and operating characteristics of the MME

The construction of the 6.1246.020 Multi-mode electrode is shown in

Fig. 8

. The
mercury in the reservoir 82 flows through the glass capillary 88 forming a drop at its
end. The mercury flow is controlled by the sealing needle 76, which can be raised
or lowered pneumatically. The different types of electrodes (HMDE, DME, SMDE)
are implemented by timed opening or closing of the mercury flow using this sealing
needle.

The operating characteristics of the MME are illustrated by

Figs. 7 and 8

. After valve

V

1

(inert gas supply) is opened, the mercury in the reservoir 82 is pressurized. In
the standby mode, a back pressure is built up in the interior of the slotted screw 75
which causes the built-in spring to press the sealing needle 76 onto the capillary
opening of the glass capillary 88 thus preventing the outflow of mercury. Switching
the valve

V

3

allows the inert gas to escape thus releasing the back pressure. The
inert gas pressure in the mercury reservoir 82 presses the sealing needle 76 fixed
to the PTFE membrane of the slotted screw 75 upwards and the mercury can now
flow out. The tapping mechanism of the DME and SMDE is triggered by brief open­ing and closing of valve

V

4

.

The mercury drops formed at the end of the capillary are very small and stable and
thus afford a very good signal/noise ratio. The mercury hermetically sealed in the
reservoir comes into contact only with inert gas and other inert materials and suf­fices for around 200'000 drops.

3 Installation

757 VA Computrace – Hardware

22

Fig. 8: Multi-mode electrode

74

75

76

77

73

78

79

80

81

82

83

84

85

87

88

72 89

86

72 Connection for inert gas supply

73 Connection for inert gas supply

(for all MME operating modes)

74 Locking ring (4.420.2920)

for slotted screw

75

75 Slotted screw (6.1247.040)

with PTFE membrane and built-in spring

76 Sealing needle (6.1247.020)

77 Screw thread

for slotted screw

75

78 Unused connection

79 Screw thread

for slotted screw

80

80 Slotted screw (4.420.2960)

for replenishing the mercury with
capillary fitted

81 Electrical contact pin for mercury

82 Mercury reservoir

83 Screw thread

for retaining nut

87

84 Insert ring (4.420.3011)

85 Sealing ring (4.420.2800)

made of silicone rubber

86 Locking ring (4.420.2870)

87 Retaining nut (4.420.2850)

88 Glass capillary (6.1226.030)

89 Screw connection

electrical contact for "WE" electrode
cable

3.3 Multi-mode electrode (MME)

757 VA Computrace – Hardware

23

3.3.2 Filling the MME with mercury

When handling mercury, it is necessary to take special precautionary
measures. These are described in detail in section 4.2.

All actions involving the electrode and mercury vessels must be
performed in or over the drip pan 92 supplied (see Fig. 10).

The Hg reservoir 82 of the multi-mode electrode 17 is filled with mercury of the
highest degree of purity (mass fraction w ≥ 0.99999) as follows:

1 Prepare multi-mode electrode

•

Unscrew locking ring 74 from slotted screw 75 (this gray PVC ring is
needed only to remove the slotted screws 75 or 80, see

section 3.3.7

and

section 3.3.9

).

•

Turn slotted screw 75 in or out of the screw thread 77 using a suitable
coin until the contact surface of the black O-ring at the Plexiglas wall (thin,
black stripe) is just visible below the metal thread 77.

•

Remove the plastic cap used as a transport safeguard from the retaining
nut 87.

•

Undo retaining nut 87 fully and remove from screw thread 83.

•

Place multi-mode electrode 17 with the capillary opening facing upwards
in the electrode holder 93 (see

Fig. 9

).

90

91

92

17

93

Hg

Fig. 9

: Adding the mercury

17

Multi-mode electrode
(6.1246.0020)

92 Drip pan (6.2711.030)

90

Syringe (6.2816.020) 93 Electrode holder

(6.2615.030)

91

Needle (6.2816.030)

3 Installation

757 VA Computrace – Hardware

24

2 Draw up mercury

•

Attach needle 91 to syringe 90.

•

Draw up 6 mL ultrapure mercury slowly and carefully using syringe 90.

3 Add mercury to MME

•

Lower syringe needle 91 into the top opening of the MME 17 between
sealing ring 85 and sealing needle 76.

•

Expel mercury slowly and carefully from the syringe to allow it to flow into
the Hg reservoir 82.

The Hg reservoir

82

must never be filled more than 2/3 full with mer-

cury.

3.3.3 Mounting the capillary

The glass capillaries

88

for the multi-mode electrode 17 are supplied separately in
a protective plastic package. After they have been unpacked, avoid any contact
whatsoever with the sensitive capillary tip. The capillary 88 is mounted in the MME
filled with mercury as described in

section 3.3.2

as follows:

1 Insert retaining nut

•

Screw retaining nut

87

into screw thread 83 until a slight resistance is

noticeable (on no account screw in retaining nut fully!).

2 Insert capillary

•

Cut open plastic package containing the glass capillary 88 on the side of
the large capillary opening using scissors (do not tear open), leave capil­lary in the package.

•

Insert glass capillary 88 directly from its protective plastic package
through the retaining nut 87 into the sealing ring 85 and push in as far as
it will go.

3 Tighten retaining nut

•

Firmly tighten retaining nut 87 by hand (do not use a tool). The glass
capillary 88 should then be centered in the opening of the retaining nut

87

.

•

If this is not the case, undo retaining nut 87 by one full turn and then
retighten by hand. When tightening, move glass capillary 88 in a circle so
that it is centered in the feedthrough of the retaining nut 87.

3.3.4 Filling the capillary without vacuum

The glass capillary

88

can normally be filled with mercury by the method described
here without vacuum. However, if difficulties regarding stability or reproducibility
arise with a capillary filled in this manner, try to fill the capillaries by the alternative
method with vacuum (

section 3.3.

5).

To fill the mounted glass capillary 88 (

section 3.3.3

) with Hg without vacuum, pro-

ceed as follows:

3.3 Multi-mode electrode (MME)

757 VA Computrace – Hardware

25

1 Install multi-mode electrode in 757 VA Computrace Stand

•

With the measuring head arm 19 tilted back, slide the empty measuring
vessel 6 into the holder 3 of the 757 VA Computrace Stand and then
lower the measuring head arm 19.

•

Carefully insert multi-mode electrode

17

in opening 55 of the measuring
head 20 (during insertion, the tip of the capillary 88 must not touch the
measuring head) and push in carefully as far as it will go. Avoid water
drops touch the tip of the capillary.

2 Connect multi-mode electrode

•

Screw FEP tubing 30 for the inert gas supply into connection 72 of the
multi-mode electrode 17.

•

Screw FEP tubing 38 for the inert gas supply into connection 73 of the
multi-mode electrode 17.

•

Attach electrode cable 16 (WE) to screw connection 89 of the multi-mode
electrode 17: push cable lug under the screw and then tighten screw
firmly.

3 Fill capillary with mercury

•

Switch on 757 VA Computrace Stand with mains switch 12 (the 757 VA
Computrace Stand must first be installed properly as described in

section

3.2

).

•

Start the VA Computrace program and click on

or

MAIN WINDOW /

Utility / Computrace control

to open the

COMPUTRACE CONTROL

window.
Then switch on the inert gas supply to the 757 VA Computrace Stand by
clicking on

DME

. This pressurizes the multi-mode electrode 17 and the

mercury begins to flow slowly out of the capillary.

•

Gently tap the MME with your finger (to remove any air bubbles) and
allow the mercury to flow out of the capillary into the empty measuring
vessel for approx. 2 min.

•

Fill measuring vessel 6 with 10 mL ultrapure water and add 1 drop KCl
solution (in pure water, mercury drops from the capillary only with diffi­culty).

•

Allow mercury to flow out of the capillary for ca. 2 min while checking the
drop formation: The drop time should be ca. 3 s.

4 Adjusting the sealing needle 76

•

Turn slotted screw

75

using a suitable coin slowly in a clockwise direction

until the mercury flow stops.

•

Open slotted screw 75 slightly in an anticlockwise direction until the
mercury flow restarts.

•

Gently tap the MME with your finger and turn the slotted screw 75 very
slowly clockwise until the mercury flow just stops. (The tapping action is
used to knock off the mercury drops so that it is easier to see whether
mercury continues to flow.)

•

Finally, turn slotted screw 75 a quarter of a turn clockwise.

3 Installation

757 VA Computrace – Hardware

26

5 Checking the MME for leaks

•

Switch on the dropping mercury electrode by selecting

DME

in the

COM-

PUTRACE CONTROL

window and clicking on . The mercury

drops freely out of the capillary.

•

Select

HMDE

and click on . A single mercury drop is formed.
Knock this off by gently tapping the MME 17 with your finger and check
that the mercury flow has really stopped. Repeat this operation several
times.

•

If mercury continues to flow, turn slotted screw 75 still further in a clock­wise direction and repeat check.

•

If it is not possible to stop the mercury flow, both the glass capillary 88
and the sealing needle 76 have to be replaced (see

section 3.3.9

).

3.3.5 Filling the capillary using vacuum

Filling of the glass capillary

88

with vacuum is advisable in all cases where difficul-

ties have been found with the method without vacuum described in

section 3.3.4

.

Filling with vacuum is especially recommended when no ultrapure Hg is available.

To fill the mounted glass capillary 88 (

section 3.3.3

) with Hg with vacuum, proceed

as follows:

1 Set up filling station

•

All actions involving the electrode and the mercury vessels must be
performed in or over the drip pan 92 supplied (see

Fig. 10

).

•

The MME

17

is placed in the electrode holder 93 for filling.

2 Connection for vacuum pump

•

For filling the capillary 88, the filling tubing 94 is required. At one end it is
fitted with a filling cone 95 for mounting on the capillary 88, and at the
other end with the tubing coupling 97 for attachment to the line for the
vacuum pump.

•

To avoid possible mercury losses, two gas wash bottles 96 are attached
to the filling tubing 94.

3 Vacuum pump

•

To draw up mercury a suitable vacuum pump is required (e.g. water jet
pump). The partial vacuum

∆

p

should be around 25 mbar.

•

A vacuum release tap must be installed at the vacuum pump or in the line
between the gas wash bottle and the pump for slowly releasing the vac­uum.

4 Mount filling tubing

•

Mount filling tubing 94 with filling cone 95 on glass capillary 88.

•

Connect filling tubing 94 with tubing coupling 97 to the two gas wash
bottles 96 and the vacuum pump (see

Fig. 10

).

3.3 Multi-mode electrode (MME)

757 VA Computrace – Hardware

27

94

95

88

17

92

93

97

96

96

Fig. 10

: Setting up the filling station

93

94

95

88

17

1

92

2

3

Fig. 11

: Filling the capillary

17

Multi-mode electrode
(6.1246.0020)

94 Filling tubing (6.1817.000)

88

Glass capillary (6.1226.030) 95 Filling cone (4.420.2860)

(part of the filling tubing 94)

92

Drip pan (6.2711.030) 96 Gas wash bottle

93 Electrode holder (6.2615.030) 97 Tubing coupling (6.1809.000)

(part of the filling tubing 94)

Vacuum
release tap

Pump

Vacuum

Vacuum

3 Installation

757 VA Computrace – Hardware

28

5 Evacuating in vertical position

•

Place multi-mode electrode 17 vertically in the electrode holder 93 (see

Fig. 11-1

).

•

Evacuate for ca. 2 min in this position.

6 Evacuating in inclined position

•

Carefully tilt multi-mode electrode 17 in the electrode holder 93 to an
inclined position and continue evacuating (see

Fig. 11-2

).

7 Release vacuum

•

As soon as mercury issues from the tip of the glass capillary 88 into the
filling tubing 94, carefully release the vacuum by opening the vacuum re­lease tap.

The filling tubing 94 must not be disconnected from the glass capillary
88 when under vacuum, otherwise the mercury which has issued from

the capillary would be sprayed onto the tubing wall and can no longer
be disposed of in drop form!

•

Tap the glass capillary 88 gently by hand so that any mercury drops at its
tip are knocked into the filling tubing 94.

•

Disconnect filling tubing

94

with filling cone 95 from glass capillary 88.

•

Place multi-mode electrode 17 in a horizontal position in the electrode
holder 93 (see

Fig. 11-3

).

From now on, the MME must be left in this position until it is installed in
the stand!

8 Install multi-mode electrode in 757 VA Computrace Stand

•

With measuring head arm 19 tilted back, push empty measuring vessel 6
into the holder 3 of the 757 VA Computrace Stand and then lower meas­uring head arm 19.

•

Carefully insert multi-mode electrode

17

in opening 55 of the measuring
head 20 (during insertion, the tip of the capillary 88 must not touch the
measuring head) and push in as far as it will go.

9 Connect multi-mode electrode

•

Screw FEP tubing 30 for the inert gas supply into connection 72 of the
multi-mode electrode 17.

•

Screw FEP tubing 38 for the inert gas supply into connection 73 of the
multi-mode electrode 17.

•

Attach electrode cable 16 (WE) to screw connection 89 of the multi-mode
electrode 17: push cable lug under the screw and then tighten screw
firmly.

3.3 Multi-mode electrode (MME)

757 VA Computrace – Hardware

29

10 Pressurize the MME

•

Switch on 757 VA Computrace Stand with mains switch 12 (the 757 VA
Computrace Stand must first be installed properly as described in

section

3.2

).

•

Start the VA Computrace program and click on

or

MAIN WINDOW /

Utility / Computrace control

to open the

COMPUTRACE CONTROL

window.
Then switch on the inert gas supply to the 757 VA Computrace Stand by
clicking on

DME

. This pressurizes the multi-mode electrode 17 and the

mercury begins to flow slowly out of the capillary.

•

Gently tap the MME with your finger (to remove any air bubbles) and
allow mercury to flow out of the capillary into the empty measuring vessel
for approx. 2 min.

•

Fill measuring vessel 6 with 10 mL ultrapure water and add 1 drop KCl
solution (in pure water, mercury drops from the capillary only with diffi­culty).

•

Allow mercury to flow out of the capillary for ca. 2 min while checking the
drop formation: The drop time should be ca. 3 s.

11 Adjusting the sealing needle 76

•

Turn slotted screw

75

using a suitable coin slowly in a clockwise direction

until the mercury flow stops.

•

Open slotted screw 75 slightly in an anticlockwise direction until the
mercury flow restarts.

•

Gently tap the MME with your finger and turn the slotted screw 75 very
slowly clockwise until the mercury flow just stops. (The tapping action is
used to knock off the mercury drop so that it is easier to see whether
mercury continues to flow.)

•

Finally, turn slotted screw 75 a quarter of a turn clockwise.

12 Checking the MME for leaks

•

Switch on the dropping mercury electrode by selecting

DME

in the

COM-

PUTRACE CONTROL

window and clicking on . The mercury

drops freely out of the capillary.

•

Select

HMDE

and click on . A single mercury drop is formed.
Knock this off by gently tapping the MME 17 with your finger and check
that the mercury flow has really stopped. Repeat this operation several
times.

•

If mercury continues to flow, turn slotted screw 75 still further in a clock­wise direction and repeat check.

•

If it is not possible to stop the mercury flow, both the glass capillary 88
and the sealing needle 76 have to be replaced (see

section 3.3.9

).

3 Installation

757 VA Computrace – Hardware

30

3.3.6 Storing the MME

On completion of the measurements, the MME is stored in the 757 VA Computrace
Stand so that the tip of the glass capillary 88 is immersed in pure water (or in the
solvent used). This prevents blockage of the capillary by crystallized salts.

An electrode treated in this manner can be taken out of the 757 VA Computrace
Stand after a few hours and stored in air for a lengthy period without suffering any
damage. Always store the MME so that the glass capillary 88 is horizontal (see

Fig.

11-3

).

3.3.7 Replenishing the mercury (without changing capillary)

The multi-mode electrode 17 can also be refilled with mercury without having to re­move the glass capillary 88.

1 Dismantle multi-mode electrode

•

Unscrew FEP tubing 30 and 38 from the MME. Disconnect electrode
cable 16 from the MME.

•

Take multi-mode electrode 17 out of the measuring head 20 and tap the
MME gently to knock off any mercury drops on the glass capillary into the
measuring vessel.

•

Place multi-mode electrode 17 horizontally in the electrode holder 93
(see

Fig. 11-3

). The slotted screw 80 is now at the top.

2 Replenish mercury

•

Unscrew slotted screw 80 using a suitable coin. If the slotted screw 80
can not be loosened by hand, screw on locking ring 74 and pull out of
the MME.

•

Draw up mercury using the syringe 90 with attached needle 91 and expel
into the Hg reservoir 82.

The Hg reservoir

82

must never be filled more than 2/3 full with mer-

cury.

•

Reinsert slotted screw 80 into screw thread 79 and screw flush to surface
using a suitable coin (this action may expel a few drops of mercury from
glass capillary 88).

Do not turn so tightly that the cemented-in steel threaded ring

79

becomes loose and hence jeopardizes the tightness and safety of the
MME!

3.3 Multi-mode electrode (MME)

757 VA Computrace – Hardware

31

3.3.8 Changing the capillary

Contamination of the glass capillary can necessitate its replacement. In such a
case, proceed as follows:

1 Remove multi-mode electrode from 757 VA Computrace

Stand

•

Unscrew FEP tubing 30 and 38 from the MME, disconnect electrode
cable 16 from MME.

•

Take multi-mode electrode 17 out of measuring head 20 while gently
tapping the MME to knock off any mercury drops on the glass capillary
into the measuring vessel.

•

Place multi-mode electrode 17 in a horizontal position in the electrode
holder 93 (see

Fig. 11-3

).

2 Unscrew slotted screw 75

•

Using a suitable coin, unscrew slotted screw 75 out of screw thread 77
until the contact surface of the black O-ring at the Plexiglas wall (thin,
black stripe) is just visible below the metal thread 77.

3 Dismantle old capillary

•

Position multi-mode electrode 17 vertically in the electrode holder 93 (see

Fig. 11-1

).

•

Undo retaining nut 87 completely by turning anticlockwise and lift up until
the lower part of the glass capillary 88 with the wide opening is visible.

•

Gently tap the glass capillary 88 to knock off any residual mercury in the
wide opening into the MME.

•

Press the retaining nut 87 downward with one hand and with your other
hand take glass capillary 88 completely out of the mount.

4 Dispose of old capillary

•

Connect filling tubing 94 with the tubing coupling 97 to the two gas wash
bottles 96 and the vacuum pump (see

Fig. 10

).

•

Insert glass capillary 88 (capillary end) in the filling cone 95 of the filling
tubing 94.

•

Remove mercury from capillary with the vacuum pump.

5 Replenish mercury if necessary

Proceed as described in

section 3.3.2

.

6 Mount new capillary

Proceed as described in

section 3.3.3

.

7 Fill capillary

Proceed as described in

section 3.3.4

or

section 3.3.5

.

3 Installation

757 VA Computrace – Hardware

32

3.3.9 Cleaning the MME

If the mercury in the multi-mode electrode is contaminated and this leads to distur­bances, the MME must be cleaned and refilled with ultrapure mercury. Proceed as
follows:

1 Remove multi-mode electrode from 757 VA Computrace

Stand

•

Unscrew FEP tubing 30 and 38 from the MME, disconnect electrode
cable 16 from MME.

•

Take multi-mode electrode 17 out of measuring head 20 while gently
tapping the MME to knock off any mercury drops on the glass capillary
into the measuring vessel.

2 Remove old mercury

•

Place multi-mode electrode 17 in a horizontal position in the electrode
holder 93 (see

Fig. 11-3

). The slotted screw 80 is now at the top.

•

Unscrew slotted screw 80 using a suitable coin.

•

Carefully turn MME and empty mercury through the threaded opening 79
into a waste container placed in the drip pan 92. While doing so, gently
tap the glass capillary 88 and the MME to ensure that all mercury flows
out of the MME.

3 Dismantle MME

•

Unscrew retaining nut 87.

•

Take glass capillary 88 out of opening 83, the sealing ring 85 and the
locking ring 86 are removed at the same time. Remove these two parts
from the glass capillary 88.

•

Remove insert ring 84 from the MME.

•

Unscrew slotted screw 75 with a suitable coin in an anticlockwise direc­tion from screw thread 77.

•

Screw locking ring 74 onto slotted screw 75 and pull out of the MME.

4 Dispose of old capillary

•

Connect filling tubing 94 with the tubing coupling 97 to the two gas wash
bottles 96 and the vacuum pump (see

Fig. 10

).

•

Insert glass capillary 88 (capillary end) in the filling cone 95 of the filling
tubing 94.

•

Remove mercury from the capillary with the vacuum pump.

5 Clean MME

•

Clean inner compartments of the MME, contact pin 81 and the screw
threads 77, 79 and 83 with a lint-free cloth.

•

Thoroughly rinse all inner compartments of the MME and the unscrewed
individual parts with dist. water and then dry with N

2

.

Do not use any organic solvents.

3.3 Multi-mode electrode (MME)

757 VA Computrace – Hardware

33

6 Replace sealing needle 76 if need be

If problems with leaks arise owing to a worn, deformed or damaged sealing
needle 76, this must be replaced. Three spare needles are supplied sepa­rately in a protective plastic package. After unpacking a needle, please avoid
any contact whatsoever with the needle tip. The spare needle 76 is installed
as follows:

•

Carefully pull old sealing needle 76 out of PTFE membrane of the slotted
screw 75.

•

Carefully insert new sealing needle 76 without tilting into the hole in the
PTFE membrane of the slotted screw 75.

When the sealing needle

76

is changed, it is always necessary to

change the glass capillary

88

!

7 Replace sealing ring 85 if need be

•

If the sealing ring 85 is contaminated or damaged in any way, it must be
replaced for the subsequent assembly of the MME. Two new sealing
rings 85 are enclosed in the package with the 6.1226.030 glass capillar­ies.

8 Reassemble MME

•

Screw slotted screw 80 using a suitable coin flush into screw thread 79.

Do not turn so tightly that the cemented-in steel threaded ring

79

becomes loose and hence jeopardizes the tightness and safety of the
MME!

•

Using a suitable coin, screw slotted screw 75 into the screw thread 77
until the contact surface of the black O-ring at the Plexiglas wall (thin,
black stripe) is just visible below the metal thread 77.

•

Place multi-mode electrode 17 with the opening 83 facing upwards in the
electrode holder 93 (see

Fig. 11-1

).

•

Insert insert ring 84 in opening 83.

•

Push sealing ring 85 onto locking ring 86 and insert both in the opening

83

.

•

Screw retaining nut 87 by hand into screw thread 83 until a slight resis­tance is felt.

9 Add mercury

Proceed as described in

section 3.3.2

.

10 Mount new capillary

Proceed as described in

section 3.3.3

.

11 Fill capillary

Proceed as described in

section 3.3.4

or

section 3.3.5

.

3 Installation

757 VA Computrace – Hardware

34

3.4 Rotating disk electrode (RDE)

The rotating disk electrode (RDE) is available as an option and can be used in
place of the MME in the 757 VA Computrace Stand with different electrode tips as a
working electrode. The following accessories have to be ordered (see also

section

6.2

):

• 6.1246.000 Drive shaft for rotating electrode

• 6.1204.XXX Electrode tip for rotating electrode

6.1204.100 Ultra Trace Graphite

6.1204.110 GC (Glassy Carbon)

6.1204.120 Pt

6.1204.130 Ag

6.1204.140 Au for Hg determination

6.1204.150 Au for As determination

• 6.2709.040 Stopper for closing the MME opening

• 6.2802.000 Polishing kit for 6.1204.XXX Electrode tips

(Pt, Ag, Au, GC)

• 6.2827.000 Trimming tool for 6.1204.100 Electrode tip
(Graphite)

It is recommended to use RDE tips (except Pt) only together with a
glassy carbon auxiliary electrode!

3.4.1 Construction and startup of the RDE

The rotating disk electrode RDE comprises the two parts drive shaft

100

(6.1246.000) and electrode tip

99

(6.1204.XXX), which must be screwed together.

The procedure for installing the RDE in the measuring head arm of the 757 VA
Computrace Stand is described in detail in

section 3.2.4

. The fully equipped meas-

uring head arm with the RDE is illustrated in

Fig. 12

.

3.4.2 Regenerating the RDE

The RDE is a solid electrode with a stationary surface. This becomes contaminated
with the products of the electrode redox processes with increasing use. The surface
of the 6.1204.XXX electrode tips (Pt, Ag, Au, GC) must therefore be regenerated
from time to time by mechanical cleaning with extremely fine aluminum oxide pow­der. Proceed as follows:

•

Affix polishing cloth (part of 6.2802.000 Polishing kit) to a flat surface (e.g. to the
bottom of a Petri dish) then add a little Al

2O3

powder (part of 6.2802.000 Polish-

ing kit) and dist. H

2

O to form a thick paste.

•

Polish electrode tip by hand in the paste for ca. 10 s with small, circular move­ments.

•

Rinse electrode tip with dist. H

2

O, immerse in diluted HCl for ca. 10 s, rinse

again with dist. H

2

O and then dry with a cloth or filter paper.

Regeneration of the 6.1204.100 Ultra Trace Graphite Electrode Tip depends on its
use (mercury film or adsorptive stripping voltammetry). The procedure is described
in detail in the Application Bulletins available for the determinations with this elec­trode.

3.4 Rotating disk electrode (RDE)

757 VA Computrace – Hardware

35

34 35 36 37 16 30 98

2831 38 100 99

2

39

19

20

39

Fig. 12

: Measuring head arm with rotating disk electrode (RDE)

2

Stopper (6.2709.080)

to close the pipetting opening

36 FEP tubing (6.1805.180)

for inert gas supply to tapping mecha­nism (attached)

16 Electrode cable ”WE”

connection for working electr. (RDE)

37 Electrode cable ”AE”

connection for auxiliary electrode

39

19 Measuring head arm

carrier plate with permanently at­tached measuring head, raisable

38 FEP tubing (6.1805.180)

20 Measuring head

measuring vessel upper half made of
PTFE; with openings for electrodes,
stirrer, gas and liquid supply lines

39 Auxiliary electrode

details, see

section 3.6

28 Drive belt (6.1244.020)

connection between drive wheel 31
and drive shaft

100

98 Stopper (6.2709.040)

for closing the MME opening and to
accommodate the two lengths of FEP
tubing 30 and

38

30 FEP tubing (6.1805.180) 99 Electrode tip (6.1204.XXX)

for RDE

31 Drive wheel of drive motor 100 Drive shaft (6.1246.000)

for RDE

35 FEP tubing (6.1805.090)

for inert gas lead-off (attached)

3 Installation

757 VA Computrace – Hardware

36

3.5 Reference electrode

3.5.1 Construction

The complete reference electrode (RE) 22 comprises two parts:

• 6.0728.0X0 Ag/AgCl reference system (101)

with ceramic diaphragm type D, diameter = 1 mm

6.0728.020 Reference system: Ag/AgCl/c(KCl) = 3 mol/L;
supplied in a holder filled with c(KCl) = 3 mol/L
as standard

6.0728.010 Reference system: Ag/AgCl
supplied dry (option)

• 6.1245.010 Electrolyte vessel (102)

with ceramic diaphragm type D, diameter=3 mm; holds
a second electrolyte solution (bridge electrolyte) and
thus forms with the 6.0728.020 Reference system a
complete reference electrode in the so-called double
junction construction.

The construction of the reference electrode and the designations of the individual
parts are shown in

Fig. 13

.

22

102

109

110

111

101

103

104

105

106

107

108

Fig. 13

: Construction of the reference electrode

22 Reference electrode

101 Reference system (6.0728.0X0)

102 Electrolyte vessel (6.1245.010)

103 Electrical connection for cable

"AE"

104 Vent opening

105 Ag/AgCl filling

106 Electrolyte compartment with

internal electrolyte

107 Diaphragm support made of

PCTFE

108 Diaphragm

109 Vent opening

110 Electrolyte compartment with

bridge electrolyte

111 Diaphragm

3.5 Reference electrode

757 VA Computrace – Hardware

37

3.5.2 Startup procedure

The reference electrode 22 is supplied in modular form as the reference system

101

and the electrolyte vessel

102

and has first to be filled and assembled as fol-

lows:

1 Add internal electrolyte

Filling of the reference system is necessary only when the optional

6.0728.010 Reference system supplied dry is used, if the internal electrolyte
solution has to be renewed or if gas bubbles interrupt the electrical connec­tion.

•

Hold reference system

101

so that diaphragm

108

faces upwards.

•

Unscrew diaphragm support

107

.

•

Fill electrolyte compartment

106

completely with the desired internal

electrolyte. Expel any air bubbles by tapping shaft gently.

•

Screw diaphragm support

107

back on, the electrolyte solution thus

displaced is expelled through the vent opening

104

.

2 Add bridge electrolyte

•

Fill internal compartment

110

of the electrolyte vessel

102

with a suitable
bridge electrolyte whose composition depends on the analyses to be per­formed (aqueous or non-aqueous solution, composition of the supporting
electrolyte, etc.).

If you use the same solution for the bridge electrolyte and the internal
electrolyte (single-junction operation), the inner diaphragm 108 can
be omitted to reduce the electrical resistance: Unscrew diaphragm
support 107 with diaphragm 108 from the reference system 101.

3 Screw reference electrode together

•

Insert the filled reference system

101

in the vessel

102

filled with bridge
electrolyte and screw tight. The electrolyte solution thus displaced is ex­pelled through the vent opening

109

.

4 Install reference electrode in 757 VA Computrace Stand and

connect

•

Insert reference electrode

22

in opening 58 of the measuring head 20

(see

Fig. 6

).

•

Attach electrode cable

27

(RE) to reference electrode 22:

push cable lug under the screw and then tighten screw firmly.

•

Turn reference electrode 22 so that the electrode cable 27 points to the
rear and not to the side (in the latter position it may become kinked and
damaged when cover 1 is closed).

•

Wait approx. 20 min before first measurement (it takes some time for a
new reference electrode to become wet).

3 Installation

757 VA Computrace – Hardware

38

3.6 Auxiliary electrode

3.6.1 Construction

The following electrodes can be used as the auxiliary electrode 39 (AE):

• 6.0343.000 Pt auxiliary electrode

supplied as standard

• 6.1241.020 Electrode holder

and

6.1247.000 Glassy carbon tip

together form the glassy carbon auxiliary electrode
available as an option

The construction of the two auxiliary electrodes and the designations of the individ­ual parts are shown in

Fig. 14

.

3.6.2 Startup procedure

The 6.0343.000 Pt auxiliary electrode supplied as standard can be inserted directly
in the 757 VA Computrace Stand (→ 2), whereas the GC auxiliary electrode avail­able as an option must first be assembled (→ 1):

1 Assembly of the GC auxiliary electrode

•

Insert glassy carbon tip

117

through the locking ring

116

into the elec-

trode holder

115

as far as it will go.

Glassy carbon is a brittle, easily breakable material and must therefore
be inserted carefully into the electrode holder and handled gently.

If the GC tip breaks, the part remaining in the holder can be removed
by pulling out the locking ring 116.

2 Install auxiliary electrode in 757 VA Computrace Stand and

connect

•

Insert auxiliary electrode

39

in opening 51 of the measuring head 20

(see

Fig. 6

).

•

Attach electrode cable

37

(AE) to auxiliary electrode 39:

Push cable plug under the screw and tighten screw firmly.

•

Turn auxiliary electrode 39 so that the electrode cable 37 points to the
rear and not to the side (in the latter position it may become kinked and
damaged when cover 1 is closed).

3.7 Stirrer

757 VA Computrace – Hardware

39

39

112

115

116

117

112

113

114

Fig. 14

: Construction of the auxiliary electrode

3.7 Stirrer

The complete stirrer comprises two parts (see also

Fig. 4

):

• 6.1246.010 Drive shaft (24)

• 6.1204.090 Stirrer tip (42)

The startup procedure for the stirrer is as follows:

1 Assemble stirrer

•

Screw stirrer tip 42 firmly to drive shaft 24.

2 Insert stirrer in 757 VA Computrace Stand and connect

•

Insert complete stirrer in opening 60 of the measuring head 20 as far as it
will go (see

Fig. 6

).

•

Stretch drive belt 28 between drive wheel 31 and drive shaft 24 of the
stirrer (see

Fig. 6

).

39 Auxiliary electrode

112 Electrical connection for

cable "AE"

113 Pt Auxiliary electrode

(6.0343.000)

114 Pt tip

(permanently attached)

115 Electrode holder

(6.1241.020)

116 Locking ring

117 Glassy carbon tip

(6.1247.000)

3 Installation

757 VA Computrace – Hardware

40

3.8 Connection of 765 Dosimats

The predecessor model 665 Dosimat can also be connected instead
of the 765 Dosimat.

Up to five 765 Dosimats can be attached to the 757 VA Computrace Stand for the
automatic addition of standard and auxiliary solutions. For the connection of 1 or 2
Dosimats, the 6.2141.080 Cable is used, for the connection of up to 5 Dosimats, the

6.9921.170 cable. The 765 Dosimat and the accessories needed have the following
ordering designations (see also

section 6.2

):

• 2.765.0010 Dosimat

• 6.2141.080 Cable 757 – 2 × 765

• 6.3014.XXX Exchange unit

, with PCTFE/PTFE flat stopcock

6.3014.153 burette volume V = 5 mL

6.3014.213 burette volume V = 10 mL

6.3014.223 burette volume V = 20 mL

6.3014.253 burette volume V = 50 mL

The choice of Exchange unit depends on the volume of liquid the Dosimat should
dispense. A burette volume of 5 mL is recommended for additions in the µL range
(standard additions solutions), a burette volume of 10 mL or higher is recom­mended for additions in the mL range (auxiliary solutions).

This section describes the connection procedure; further details on the 765 Dosimat
and the various Exchange units can be found in the

765 Instructions for Use

.

3.8.1 Electrical connection and setup

Before a 765 Dosimat is attached to the 757 VA Computrace Stand,
the 757 VA Computrace Stand must be switched off using the mains
switch 12.

One or two 765 Dosimats are connected to the 757 VA Computrace Stand with the
optionally available

6.2141.080 Cable

. The "A" socket of the 765 Dosimat is con-

nected to the socket "Remote" 15 of the 757 VA Computrace Stand.

For hardware settings of the 765 Dosimats in the VA Computrace program see

757

Software Manual

.

For settings (dosing rate, filling rate, etc.) and manual operation (manual filling or
dispensing) using the keyboard of the 765 Dosimat, see

765 Instructions for Use

.

If 765 Dosimats are connected to the 757 VA Computrace Stand, the
instruments must always be switched on in the sequence 765

→

757

→

PC.

3.8 Connection of 765 Dosimats

757 VA Computrace – Hardware

41

3.8.2 Tubing connection

For the addition of standard or auxiliary solutions into the measuring vessel of the
757 VA Computrace Stand the 4-way microtip 26 (6.1824.000) can be used. It is fit­ted with 4 lengths of PTFE tubing with connection nipples for direct attachment to
the Exchange unit of the 765 Dosimat. To ready the 765 Dosimat for automatic dis­pensing, proceed as follows:

1 Mount Exchange unit on 765 Dosimat

•

Procedure, see section

5 of 765 Instructions for Use

.

2 Insert 4-way microtip in 757 VA Computrace Stand

(see

section

3.2.4)

•

Remove stopper from nipple 23 and insert 4-way microtip 26 into nipple

23

as far as it will go (see

Figs 3 and 6

).

•

Tighten nipple 23 using a 6.2739.000 Wrench (accessory of 6.3014.XXX
Exchange unit) so that the 4-way microtip 26 can no longer move.

•

Pull the 4 lengths of PTFE tubing of the 4-way microtip 26 in succession
from above through the opening 65.

3 Connect PTFE tubing to Exchange unit

•

Unscrew the attached 6.1805.100 FEP Tubing
(L = 40 cm) from connection 2 (connection for burette
tip) of the flat stopcock on the Exchange unit mounted
on the Dosimat.

•

Screw connection nipple of the PTFE tubing of the
4-way microtip 26 onto connection 2 of the flat stop­cock on the Exchange unit mounted on the Dosimat.

2

4 Close unused PTFE tubings

•

Screw a 6.1808.000 Coupling (accessory of 757 VA Computrace Stand)
on each unused PTFE tubing of the 4-way microtip 26.

•

Screw a 6.1446.040 Dummy stopper (accessory of 757 VA Computrace
Stand) on each 6.1808.000 Coupling.

5 Initialize Dosimat(s)

•

Switch on the 765 Dosimat.

•

Switch on the 757 VA Computrace Stand using the mains switch 12.

•

Switch on the PC and start the VA Computrace program.

•

Click on

or

MAIN WINDOW / Utility / Dosimat control

to open the

DOSI-

MAT CONTROL

window.

•

Select the desired Dosimat in the

Burette

field.

•

Click the

button to empty and refill the exchange unit in-

stalled on the Dosimat. Repeat this procedure two times.

•

Check if there are air bubbles left in the glass cylinder of the exchange
unit. If this is the case, repeat the flushing procedure by clicking the

button.

•

Close the

DOSIMAT CONTROL

window.

3 Installation

757 VA Computrace – Hardware

42

3.8.3 Changing the Exchange unit

The Exchange unit mounted on the 765 Dosimat can be changed only in the ex­change position which is reached after filling. Please proceed as follows:

1 Fill exchange unit

At the start of the VA Computrace program, the exchange unit is automati­cally filled. So this step is only necessary if the Dosimat has already been
used during the running program session.

•

Click on

or

MAIN WINDOW / Utility / Dosimat control

to open the

DOSI-

MAT CONTROL

window.

•

Select the desired Dosimat in the

Burette

field.

•

Click the

button to fill the exchange unit installed on the

Dosimat.

2 Change Exchange unit

•

Unscrew connection nipple of the PTFE tubing of the 4-way microtip 26
from connection 2 and take off old Exchange unit.

•

Mount new Exchange unit on Dosimat and screw connection nipple of the
PTFE tubing of the 4-way microtip 26 onto connection 2 of the flat stop­cock on the Exchange unit.

3 Enter new volume of Exchange unit

If the volume of the new Exchange unit is different to the volume of the old
one, proceed as follows:

•

Select

MAIN WINDOW / Settings / General Settings.

Open the

Hardware

tab in

the

GENERAL SETTINGS

window.

•

Enter the new

Volume

of the Exchange unit installed on the 765 Dosimat.

•

Close the VA Computrace software by clicking on

or selecting

File /

Exit

.

•

Restart the VA Computrace software.

4 Initialize Dosimat(s)

•

Click on

or

MAIN WINDOW / Utility / Dosimat control

to open the

DOSI-

MAT CONTROL

window.

•

Select the desired Dosimat in the

Burette

field.

•

Click the

button to empty and refill the exchange unit in-

stalled on the Dosimat. Repeat this procedure two times.

•

Check if there are air bubbles left in the glass cylinder of the exchange
unit. If this is the case, repeat the flushing procedure by clicking the

button.

•

Close the

DOSIMAT CONTROL

window.

3.9 Connection of the 813 Compact Autosampler

757 VA Computrace – Hardware

43

3.9 Connection of the 813 Compact Autosampler

With the 813 Compact Autosampler connected to the 757 VA Computrace Stand,
max. 18 samples can be transferred to the measuring vessel at the 757 VA Com­putrace Stand. After each measurement, the measuring vessel is rinsed by means
of two 772 Pump Units connected to a 731 Relay Box. For operation of this sample
changer and the automatic addition of standard addition and auxiliary solutions by
means of 765 Dosimats, the following instruments and accessory parts are needed
(see also

section 6.2

):

Quant. Order no. Instrument/Accessory

1 2.813.0020 813 Compact Autosampler for VA applications

1 2.731.0010 731 Relay Box

2 2.772.0010 772 Pump Unit

1 6.2141.150 Cable 813–757–731

1 6.5323.010 Rinsing equipment for VA

1…5 2.765.0010 765 Dosimat

1…5 6.3014.153 Exchange unit 5 mL (for addition solutions)

1…5 6.3014.213 Exchange unit 10 mL (for auxiliary solutions)

1 6.2141.080

Cable 757–2×765

or

1 6.9921.170

Cable 757–5×765

This section describes the procedure for the connection of 813 Compact Autosam­pler, 731 Relay Box and 772 Pump Units. For the connection of 765 Dosimats, see

section 3.8

.

3.9.1 Electrical connection

Before any instruments are attached to the 757 VA Computrace Stand,
the 757 VA Computrace Stand must be switched off using the mains
switch 12.

The 813 Compact Autosampler is connected to the socket "Remote" 15 of the 757
VA Computrace Stand with the optionally available

6.2141.150 Cable

(see

Fig. 15

).
The second end of the 6.2141.150 cable is used to connect the 731 Relay Box. The
third end of the 6.2141.150 cable is used to connect 765 Dosimats with the

6.2141.080 cable (1...2 Dosimats) or the 6.9921.170 cable (1...5 Dosimats). At the
813 Compact Autosampler, "

Method 2

" must be set (procedure see

Instructions for

Use 813

).

At the connection "DC1" of the 731 Relay Box, a 772 Pump Unit is connected as

si-

phoning pump

, at the connection "DC2", a 772 Pump Unit is connected as

rinsing

pump

(see

Instruction for Use 731

and

772

). The output voltage of the 731 Relay

Box must be set to

+24 V

(default setting, see

section 2.3, Instruction for Use 713

).
Additionally, the following settings for remote address selection must be done:

DC1: 9

(Siphoning pump)

DC2: A

(Rinsing pump)

3 Installation

757 VA Computrace – Hardware

44

757

813

765

772 772

731

6.2141.150 Cable

6.2141.080 Cable

Fig. 15

: Electrical connection of the 813 Compact Autosampler

772

772

D

ES FUSIBLES DE 250V

USE ONLY WITH 250V

UNIQUEMENT AVEC

FUSES/EMPLOYER

100-120V

220-240V

O

I

6.1822.410

6.1831.050

6.1819.010 (2 cm)

757

6.1805.1002x6.1808.000 6.1805.020

6.1805.180

6.1819.010 (3 cm)

6.1819.010 (2 cm)

6.1819.010

2x6.1820.020

6.1805.530

6.1805.530

2x6.1820.020

2x6.1820.050

2x6.1820.050

6.1805.530

6.1826.100

6.1826.100

6.1805.530

6.1602.105

6.1618.050

6.1829.020

6.1602.105

6.1618.050

6.1819.020 (10 cm)

Rinsing
solution

Waste

Rinsing pump

Aspiration pump

Fig. 16

: Tubing connections for operation of the 813 Compact Autosampler

3.9 Connection of the 813 Compact Autosampler

757 VA Computrace – Hardware

45

34

118

119

20

120

121

4345

2 cm

3 cm

2 cm

44

Fig. 17

: Installation of accessories for rinsing and siphoning off

19 Measuring head arm

20 Measuring head

34 FEP tubing (6.1805.100)

for waste solution lead-off (attached)

43 PTFE tube (6.1819.010)

for supply of the waste solution to gas
wash bottle

44

44 Gas wash bottle (6.2405.030)

for separating mercury from the waste
solution (attached)

45 PTFE tube (6.1819.010)

for siphoning off the waste solution
from gas wash bottle 44 (attached)

118 FEP tubing (6.1805.180)

for transferring the waste solution to
gas wash bottle 44

119 FEP tubing (6.1805.100)

for supply of the rinsing solution

120 PTFE tube (6.1819.010)

for introduction of the rinsing solution
to the measuring vessel

121 PTFE tube (6.1819.010)

for siphoning-off the waste solution

3 Installation

757 VA Computrace – Hardware

46

max. 0.5 mm

3.9.2 Tubing connections

For operation of the 757 VA Computrace Stand with 813 Compact Autosampler and
772 Pump Units, the accessories and tubing connections must be installed accord­ing to

Fig. 16

. Proceed as follows:

1 Install accessories at 757 VA Computrace Stand

•

Instead of the 6.1415.210 measuring vessel, install the 6.1456.210 meas­uring vessel at the 757 VA Computrace Stand.

•

Cut PFTE tube 43 (6.1819.010) inserted in opening 67 of the measuring
head 20 to a length of

max. 30 mm

(see

Fig. 6

and

17).

•

Cut PFTE tube 45 (6.1819.010) inserted in opening 66 of the measuring
head 20 to a length of

max. 20 mm.

•

Cut PFTE tube

120

(6.1819.010) to a length of

max. 20 mm

and insert

from above in opening 53 of the measuring head 20.

•

Cut the bottom end of PFTE tube

121

(6.1819.010) diagonally and insert
from above in opening 52 of the measuring head 20. To ensure that the
solution is siphoned off as completely as possible, the end of the tube
must be located in the deepest part of the 6.1456.210 measuring vessel
(left rear when viewed from front).

•

Screw FEP tubing

118

(6.1805.180) into threaded openings 52 and 66.

•

Screw FEP tubing

119

(6.1805.100) into threaded opening 53 of the
measuring head 20. Screw a 6.1808.000 tubing coupling to the other end
of FEP tubing

119

and insert the coupling in a slot of the tubing holder at

the rear of the 757 VA Computrace Stand.

2 Connect 813 Compact Autosampler

•

Install accessories at 813 Compact Auto­sampler (see

Instructions for Use 813

).

•

Adjust 6.1835.030 Pipetting needle at the
757 Compact Autosampler to ensure that
the lower end of the needle is positioned
max. 0.5 mm above the bottom of the
sample vessel (see

Fig. 18

). This is essen­tial to guarantee a complete transfer of the
sample from the sample vessel into the
measuring vessel of the 757 VA Com­putrace Stand.

•

Insert 6.1822.410 transfer tubing connected
to 6.1826.020 pump tubing from above into
opening 57 of the measuring head 20 at
the 757 VA Computrace Stand (see

Fig. 6

)

and fix it by screwing the nipple.

Fig. 18

: Adjusting the

pipetting needle

3.9 Connection of the 813 Compact Autosampler

757 VA Computrace – Hardware

47

3 Connect 772 siphoning pump

•

Cut 6.1826.100 pump tubing to a length of ca. 17 cm.

•

Attach two 6.1820.050 tubing connectors to both ends of the 6.1826.100
pump tubing and install it at the first 772 Pump Unit (see

Instructions for

Use 772

).

•

Screw a 6.1820.020 thread onto both 6.1820.050 connectors.

•

Using a 6.1805.530 FEP tubing, connect the lower end of the pump
tubing on the siphoning pump to the 6.1808.000 connector at the 757 VA
Computrace Stand, to which the FEP tubing 34 is connected (see

Fig. 16

and

Fig. 17

).

4 Connect 772 rinsing pump

•

Cut 6.1826.100 pump tubing to a length of ca. 17 cm.

•

Attach two 6.1820.050 tubing connectors to both ends of the 6.1826.100
pump tubing and install it at the second 772 Pump Unit (see

Instructions

for Use 772

).

•

Screw a 6.1820.020 thread onto both 6.1820.050 connectors.

•

Using a 6.1805.530 FEP tubing, connect the upper end of the pump
tubing on the rinsing pump to the 6.1808.000 connector at the 757 VA
Computrace Stand, to which the FEP tubing

119

is connected (see

Fig.

16

and

Fig. 17

).

5 Connect waste container

•

Unscrew red filling connection from first 6.1621.000 container.

•

Screw 6.1618.050 threaded adapter to the container.

•

Screw 6.1602.105 siphon onto 6.1618.050 threaded adapter.

•

Cut 6.1819.020 FEP tube to a length of ca. 10 cm and insert from above
into the smallest opening of the 6.1602.105 siphon.

•

Screw a 6.1805.530 FEP tubing into this opening of the 6.1602.105
siphon.

•

Attach the other end of the 6.1805.530 FEP tubing at the upper end of the
pump tubing of the siphoning pump (see

Fig. 16

).

6 Connect storage container

•

Unscrew red filling connection from second 6.1621.000 container.

•

Using a funnel, add max. 10 L rinsing solution (normally ultrapure water
acidified with 100 µL conc. HCl/L) to the storage container through the
small vent opening.

•

Screw 6.1618.050 threaded adapter to the container.

•

Screw 6.1602.105 siphon onto 6.1618.050 threaded adapter.

•

Remove screw nipple from 6.1829.020 FEP tube and insert it from above
into the smallest opening of the 6.1602.105 siphon.

•

Screw a 6.1805.530 FEP tubing into this opening of the 6.1602.105
siphon.

•

Attach the other end of the 6.1805.530 FEP tubing at the lower end of the
pump tubing of the rinsing pump (see

Fig. 16

).

3 Installation

757 VA Computrace – Hardware

48

3.9.3 Software settings

Before putting into operation the 757 VA Computrace Stand with the 813 Compact
Autosampler, the following settings have to be made in the "

757 VA Computrace

2.0

" software program:

1 Set Dosimat parameters

•

Click on

MAIN WINDOW / Settings / General settings

and select the

Hardware

tab.

•

For each Dosimat connected to the remote interface of the 757 VA Com­putrace Stand, check the

Dosimat no.

checkbox and enter the

Volume

of

the exchange unit installed on the Dosimat and the

Dose rate

of the Dosi-

mat.

•

Define the addition or predose solutions for the desired method in the

DOSIMATS

window (procedure see

Software Manual, section 5.2

).

•

Fill the exchange units of the Dosimats with the desired solutions and
make sure that there are no gas bubbles in the glass cylinders using the

button in the

DOSIMAT CONTROL

window (see

section 6.2

,

Software Manual

).

3.9 Connection of the 813 Compact Autosampler

757 VA Computrace – Hardware

49

2 Set automation parameters

•

Click on

MAIN WINDOW / Settings / General settings

and select the

Automa-

tion

tab.

•

Enable the

Use Autosampler

option, modify the automation parameters as

desired and close the

GENERAL SETTINGS

window.

•

Close the "757 VA Computrace 2.0" program and restart it.

3 Test automation parameters

•

Fill two sample vessels with water and place them one after the other on
the sample rack of the 813 Compact Autosampler.

•

Click on

MAIN WINDOW / Settings / General settings

and select the

Automa-

tion

tab.

•

Click on

, check the automation parameters and modifiy
them if need be. The default settings can be normally used for samples
with 10 mL volume:

3 Installation

757 VA Computrace – Hardware

50

3.9.4 Operation of the 813 Compact Autosampler

After installation of the instruments according to

sections 3.9.1

...

3.9.3

sample series
using the 813 Compact Autosampler can be started. Proceed always in the follow­ing sequence:

1 Switch on instruments

•

Switch on Dosimats and 757 VA Computrace Stand.

•

Switch on 813 Compact Autosampler and 731 Relay Box.

•

Switch on PC.

•

Start 757 VA Computrace software (see

Software Manual, section 2.2

).

2 Load and modify method

•

Click on

or

MAIN WINDOW / Mode / Determination

.

•

Click on

or

MAIN WINDOW / Window / Working method specification

to

open the

WORKING METHOD SPECIFICATIONS

window.

•

Load the desired method in the

WORKING METHOD SPECIFICATIONS

window.

•

If desired, modify the loaded method (details see

Software Manual

).

3 Load and modify sample table

•

Click on

or

MAIN WINDOW / Window / Sample table

to open the

SAMPLE

TABLE

window.

•

Load the desired sample table or edit the current sample table (details
see

Software Manual

).

4 Place samples on 813 Compact Autosampler

•

Transfer the desired sample amount (5...10 mL) into the sample vessels
and place them at the odd positions on the sample rack of the 813 Com­pact Autosampler.

•

For each sample vessel, place a vessel filled with rinsing solution at the
following even position (volume rinsing solution = volume sample solu­tion).

5 Start determination

•

Click on

or

MAIN WINDOW / Window / Monitor

to open the

MONITOR

window.

•

Start the measurement by clicking the

icon in the

MAIN WINDOW

or

the

button in the

MONITORING

window.

•

Press the "START" button on the keypad of the 813 Compact Autosam­pler.

•

Follow the instructions in the appearing message windows.

4.1 Electrical safety

757 VA Computrace – Hardware

51

4 Safety

4.1 Electrical safety

While electrical safety in the handling of the 757 VA Computrace Stand is assured in
the context of the specifications IEC 61010-1 (protection class 1), the following
points should be noted:

• Mains connection

Setting mains connection must be effected in accordance with the
instructions in section 3.2.1.

• Opening the instrument

When the 757 VA Computrace Stand is connected to the power
supply, the instrument may not be opened nor parts of them be
removed, otherwise there is a danger of coming into contact with
components which are live. Before you open the 757 VA Computrace
Stand to change components or for maintenance or repair work,
always switch on the instrument by setting the mains switch

12

to the
ON position and then disconnect the mains cable from the mains
connection plug

13

of the 757 VA Computrace Stand !

• Protection against static charges

Electronic components are sensitive to static charging and can be
destroyed by discharges. Before you touch any of the components
inside the 757 VA Computrace Stand, you should earth yourself and
any tools you are using by touching an earthed object (e.g. green
housing of the instrument or a radiator) to eliminate any static charges
which exist.

4 Safety

757 VA Computrace – Hardware

52

4.2 Safety considerations concerning mercury

4.2.1 Properties of mercury

The most important properties of mercury (Hg) are listed in the Table below. This
compilation allows the following summary:

•

Mercury is a

heavy metal

with a very high density and is

liquid

at room tem-

perature.

•

Mercury is mobile at room temperature and tends to

form drops

because of
its high surface tension. The surface tension is around 6 times greater than
that of water, Hg is thus not wetted by water.

•

Mercury has a relatively

high electrical conductivity

(at room temperature it

is only some 60 times lower than that of silver).

•

Mercury has a relatively

high vapor pressure

compared with other metals.
Mercury vapor is some seven times heavier than air (so that it sinks rapidly
and specifically to the floor).

•

The

odor threshold is very high

relative to the threshold limit value (TLV).

•

Air saturated with Hg vapor (which naturally does not occur in practice) con­tains approximately 250 times the amount of Hg specified by the TLV at room
temperature.

Properties of mercury

Property Value Ref.

Density ρ (liquid mercury) 13.5451 g/cm3 (at Θ = 0 ° C) [1]

Density ρ (mercury vapor) 8.959 g/dm3 (at Θ = 0 ° C) [2]

Melting point

Θ

F

–38.86 ° C (at p

air

= 1.01325 bar) [3]

Melting enthalpy ∆HF 2.295 kJ/mol (at p

air

= 1.01325 bar) [3]

Boiling point

Θ

V

356.73 ° C (at p

air

= 1.01325 bar) [3]

Boiling enthalpy ∆HF 59.1 kJ/mol (at p

air

= 1.01325 bar) [3]

Vapor pressure p 0.0253 Pa (at

Θ

= 0 ° C)

0.17 Pa (at Θ = 20 ° C)

0.391 Pa (at Θ = 30 ° C)

0.81 Pa (at Θ = 40 ° C)

1.69 Pa (at Θ = 50 ° C)

[2, 4]

Mass concentration ρ in air
(after reaching equilibrium)

2.0 mg/m3 (at Θ = 0 ° C)

13.6 mg/m3 (at Θ = 20 ° C)

29.6 mg/m3 (at Θ = 30 ° C)

62.7 mg/m3 (at Θ = 40 ° C)
126 mg/m3 (at Θ = 50 ° C)

[2, 4]

Evaporation rate 85 µg/h·cm2 (at Θ = 25 ° C) [2]

Surface tension σ 4.67·10–3 N/cm (at Θ = 20 ° C) [5]

Electrical conductivity κ 1.044·104 S/cm (at Θ = 20 ° C) [6]

Odor threshold 13 mg/m3 [2]

Threshold limit value (TLV) for air

for mercury
for organic mercury com-

pounds (calculated as Hg)

0.1 mg/m3

0.01 mg/m3

[4, 7]

[2, 4, 7]

4.2 Safety considerations concerning mercury

757 VA Computrace – Hardware

53

4.2.2 Toxicity of mercury and its compounds

Mercury and its compounds are toxic since they react with enzymes containing sul­fur and decompose them with the formation of HgS. The toxicity depends on the
chemical and physical state of the mercury [4, 8 – 10]:

• Metallic liquid mercury

is readily resorbed by the skin and finds its way
through glandular passages into lower skin regions where it is oxidized and
carried on as a salt.

•

The low-solubility

mercury (I) compounds

and metallic mercury in the form
of a coherent liquid have low toxicity when taken up orally (but not through the
skin!).

• Mercury (II) compounds

are more readily soluble and therefore much more

toxic: LD100 (the 100% lethal dose) for oral take-up is approx. 0.2…1 g.

• Mercury vapor

is highly toxic: vapor with an Hg concentration exceeding the

TLV of 0.1 mg/m

3

air causes chronic poisoning after prolonged breathing for 5

to 8 hours per day.

Despite the large number of laboratories involved in polarographic/voltammetric
work, sensible and proper handling (see

section 4.2.3

) has ensured that not one
single case of mercury poisoning has been reported to date. The real Hg concen­trations measured in the laboratory atmosphere are consistently far below the TLV
(threshold limit value).

4.2.3 Handling of mercury

Several safety rules, described in detail in what follows, must be observed in the
handling of mercury owing to its toxicity (see

section 4.2.2

):

• Working in a fume cupboard

The handling of mercury should, if possible, always be carried out in a fume
cupboard (hood). It must be ensured that no metal drops or spilling drop on
the floor or the lab bench and that no evaporation of the metal occurs.

• Working over plastic trays

Movements with vessels containing mercury must be carried out in, or at least
above, rigid seamless trays made from plastic or enamelled metal. The sup­plied 6.2711.030 Drip pan made of polystyrene is eminently suitable for this.

• Collecting mercury from the measuring vessel

If work is performed with the MME, at the end of the determination the analy­sis solution contains mercury which must be collected for later disposal. This
can be done by collecting the analysis solutions in a large vessel and then
decanting, by filtering the analysis solutions or by siphoning off the mercury
using vacuum.

4 Safety

757 VA Computrace – Hardware

54

• Trapping of mercury drops

Single mercury drops in this drip pan or any other spilt mercury can be bound
in a simple manner by amalgamation:

−

with silver (Ag):
Metrohm drop catcher Type 6.2406.000 which is included
in the standard outfit of the 757 VA Computrace Stand

−

with tin (Sn):
e.g. the thin tin foil supplied by Merck, Darmstadt/FRG

−

with special laboratory aids:
e.g. Mercurisorb-Roth from Roth, Karlsruhe/FRG; e.g. Mercury
Sponge and Resisorb from Baker, Phillipsburg, N.J./USA

• Empty reservoir of mercury trap regularly

The storage container 4 of the 6.2406.000 mercury trap should be emptied
regularly and rinsed thoroughly several times. If the mercury trap is needed
outside the fume cupboard, a minimum safety distance of 50 cm between the
head and the mercury trap must be observed.

• Never leave mercury in open vessels

Mercury must never be left exposed to the air. The upper layer of water or
supporting electrolyte in no way suppresses nor reduces Hg evaporation [11,
12].

• Store mercury container in fume cupboard

The tightly closed mercury container as well as all parts which come into con­tact with mercury must be stored in a fume cupboard which is always
switched on.

• Use gas wash bottles when siphoning off mercury under vacuum

If mercury is siphoned off under vacuum using a water jet pump, one or two
gas wash bottles must always be connected between the vacuum pump and
the suction tube to ensure trapping of the siphoned-off mercury.

• Ventilate laboratory areas well

Rooms where work with mercury is being carried out should be thoroughly
aired from time to time.

• Dispose of mercury properly

Mercury can be cleaned by distillation [13 – 16], but the apparatus is exten­sive and the time needed considerable. For this reason, waste mercury is
normally collected in a closed container and then sent for disposal to the re­sponsible authorities in accordance with the national legal requirements.

4.2 Safety considerations concerning mercury

757 VA Computrace – Hardware

55

4.2.4 References dealing with mercury

[1] Documenta Geigy

Wissenschaftliche Tabellen

, 7. Ausgabe, Seite 210

(”Masseinheiten, Dichte”), Georg Thieme Verlag, Stuttgart (BRD), 1975

[2] Berufsgenossenschaft der chemischen Industrie (Herausgeber)

Quecksilber und seine Verbindungen

Merkblatt, Seite 3...4, Verlag Chemie, Weinheim (BRD), 1980

[3] Synowietz, C.; Schä fer, K. (Herausgeber)

Chemiker-Kalender

, 3. Aufl., 560/561, 590

Springer-Verlag, Berlin+Heidelberg (BRD), 1984

[4] Falbe, J.; Regitz, M.

Römpps-Chemie-Lexicon

, 9. Aufl., Seite 3737

Georg Thieme Verlag, Stuttgart, New York, 1992

[5] D'Ans/Lax

Taschenbuch für Chemiker und Physiker

, 3. Aufl., Band I, Seite 1...135

Springer-Verlag, Berlin+Heidelberg (BRD), 1967

[6] Weast, R.C. (Editor)

Handbook of Chemistry and Physics

, 57

th

edition, page E-84, B-32

The Chemical Rubber Publishing Co., Cleveland, Ohio (USA), 1976

[7] Roth, L.

Sicherheitsdaten MAK-Werte

, 3. Aufl.

Ecomed Verlagsgesellschaft mbH, München, 1984

[8] Mutschler, E.

Arzneimittelwirkungen

, Seite 379

Wissenschaftliche Verlagsgesellschaft, Stuttgart (BRD), 1970

[9] Auterhoff, H.

Lehrbuch der pharmazeutischen Chemie

, Seite 75

Wissenschaftliche Verlagsgesellschaft, Stuttgart (BRD), 1968

[10] Strong, L.E.

Mercury Poisoning

J. Chem. Educ. 49

(1972), 28

[11] Sanders, M.L.; Becket, R.R.

The Mercury-Water System

J. Chem. Educ. 52

(1975), 117

[12] Lo, J.M.; Wal, C.M.

Mercury Loss from Water during Storage –
Mechanisms and Prevention

Anal. Chem. 47

(1975), 1869

[13] Monaghan, C.P.; O'Brien, E.J. (Jr.); Good, M.L.

Cleaning Mercury

J. Chem Educ. 55

(1978), Fasc 11., 734

[14] Bergmeyer, H.U.

Vollautomatische Quecksilber-Waschapparatur für
den Laboratoriumsgebrauch

Chem. Ing. Techn. 22

(1950), 330

[15] Hamilton, P.B.

Continuous Mercury Still

Anal. Chem. 23

(1951), 1526

[16]

Quecksilberreinigung

GIT 6

(1962), 351

4 Safety

757 VA Computrace – Hardware

56

5 Technical data

757 VA Computrace – Hardware

57

5 Technical data

Subject to changes !
The listed technical data apply to an ambient tempera-

ture of 25°C.

Brief characterization

PC-controlled system for voltammetry, set chemical workplace with potentiostat
and measuring amplifier.

With multi-mode electrode, rotating disk electrode (RDE) as option.

Tilt-back measuring arm, integrated drip pan.

Current measurement techniques

DC

Direct Current

NP

Normal Pulse

DP

Differential Pulse

SQW

Square Wave (10 ... 2000 Hz)

AC1

Phase-sensitive Alternating Current 1

st

harmonic

(1 … 250 Hz)

AC2

Phase-sensitive Alternating Current 2

nd

harmonic

(1 … 250 Hz)

PSA

Potentiometric Stripping Analysis (chronopotentiometry)

CV

Cyclic Voltammetry (digital ramp)

Potentiostat

Output voltage (AE)

±

12 V

Output current (AE)

±

35 mA

Sweep voltage range

±

5 V

Voltage resolution

150 µV

Input impedance(RE)

R ≥ 1·10

10

Ω

Input Bias Current (RE)

±

10 pA

Noise

typ. 200 pA
Circuit for measurement of the noise:

100 nF

AE RE WE
Measurement mode: Differential Pulse

(method used: DPNoise.mth)

5 Technical data

757 VA Computrace – Hardware

58

Sweep rate

with voltage step 10 mV
CV: 0 … 30 V/s SQW, DC: 0 … 20 V/s
DP, NP: 0 … 0.5 V/s AC1, AC2: 0 … 0.02 V/s

Pulse amplitudes

AC1, AC2: 1 mV … 1 V
DP, NP: –1 … 1 V
SQW: 0.15 mV

…

1 V

Current measurement

Current ranges

100 nA … 10 mA in 6 ranges

Current resolution

0.5 % of the current range

Minimum current I

min

5 pA

Maximum current I

max

35 mA

Integration times

0.1 … 20 ms

Multi-mode electrode MME (working electrode WE)

Designation

6.1246.020

Electrode types

DME (dropping mercury electrode)
HMDE (hanging mercury drop electrode)
SMDE (static mercury drop electrode)

Drop surface

0.15 ... 0.60 mm

2

(DME and SMDE)

Glass capillary

6.1226.030 (set of 10)
internal diameter = 0.05 mm

Mercury reservoir

6 mL ≅ 81.2 g; sufficient for ca. 200'000 Hg drops

Auxiliary power

inert gas (generally nitrogen N

2

); p = 1 ± 0.2 bar

Rotating disk electrode RDE (working electrode WE, option)

Construction

6.1246.000 Drive shaft + screw-on

6.1204.XXX Electrode tips

Electrode tips

6.1204.100 Ultra trace graphite

6.1204.110 glassy carbon (GC)

6.1204.120 platinum (Pt)

6.1204.130 silver (Ag)

6.1204.140 gold (Au) for Hg determination

6.1204.150 gold (Au) for As determination

Disk diameter

2.0 +0 / –0.05 mm

Radial eccentricity ≤

0.2 mm

Regeneration

with 6.2802.000 Polishing kit

Rotational speed

200, 400, 600, ... , 3000 min

–1

Speed constancy ±

5 %

Reference electrode (RE)

Construction

double-junction; 6.0728.0X0 Ag/AgCl Ref. system +

6.1245.010 Electrolyte vessel to be filled by user

Reference system

Ag/AgCl/c(KCl) = 3 mol/L

Diaphragm

ceramic diaphragm; diameter = 3 mm

5 Technical data

757 VA Computrace – Hardware

59

Auxiliary electrode (AE)

Pt auxiliary electrode

6.0343.000 Platinum electrode

GC auxiliary electrode

(option)

6.1241.020 Electrode holder +

6.1247.000 Glassy carbon tip

Stirrer

Construction

6.1246.010 Drive shaft + screw-on

6.1204.090 Stirrer tip

Material

PTFE

Rotational speed

200, 400, 600, ... , 3000 min

–1

Speed constancy ±

5 %

Measuring vessels

6.1415.210

standard measuring vessel made of glass;
working volume = 10 ... 90 mL

6.1415.150

measuring vessel made of glass (option);
working volume = 5 ... 70 mL

6.1418.220

measuring vessel made of glass with thermostat
jacket (option); working volume = 12 ... 70 mL

6.1450.210

measuring vessel made of PFA (option)
working volume = 10 ... 90 mL

6.1456.210

measuring vessel made of glass for sample changer
operation (option); working volume = 10 ... 90 mL

6.1457.210

measuring vessel made of glass with thermostat
jacket for sample changer operation (option);
working volume = 10 ... 90 mL

Dummy Cell

Use

Checking the 757 VA Computrace Stand
Determination of the signal/noise ratio

Connections

AE auxiliary electrode
RE reference electrode
WE-L working electrode linear mode
(RC element)
WE-D working electrode differential mode
(peak/wave)

Inert gas (in general nitrogen N

2

)

Use

Operation of MME deaeration of sample solution

Required pressure p

= 1 ± 0.2 bar (this gas pressure results in a gas

flow rate of ca. 20 L/h)

Connection of Dosimats (Remote interface)

Type

665 or 765 Dosimat

Number

1...5

Plug

D-Sub with 25 pins

Manual operation

Dispensing, filling, adjustment of feed and filling rate

5 Technical data

757 VA Computrace – Hardware

60

VA Computrace Interface

Designation

6.2155.000 VA Computrace Interface

Type

Interface USB – VA Computrace Stand

Plug to 757

D-Sub with 37 pins

Mains connection

Voltage

100...240 V

Frequency

50...60 Hz

Power consumption

26 W

Fuse

2 × 1.0 ATH (to be replaced by Metrohm Service only
using the same type).
Additional electronic overload protection.

Safety specifications

Construction/testing

According to IEC 61010 / EN 61010 / UL 3101-1,
protection class 1

Safety directions

The Instructions for Use include information and
warnings which must be heeded by the user to
assure safe operation of the instrument.

Electromagnetic compatibility (EMC)

Emitted interference

Standards met:

EN55022 (class B), EN50081-1/2

Immunity to interference

Standards met:

IEC61000-4-2 (level 4), IEC61000-4-3 (level 2),
IEC61000-4-4 (level 4), IEC61000-4-5 (level 2/3),
IEC61000-4-6 (level 3), IEC61000-4-8,
IEC61000-4-11, ENV50204, EN50082-1/2

Ambient temperature

Nominal operating range

0…+45 ° C

Storage, transport

–40…+70 ° C

Housing

Material of cover

Polyurethane rigid foam (PUR) with fire protection for
fire class UL94VO, FCH-free

Material of base

Steel, enamelled

Material of measuring
head arm

Steel, enamelled

Dimensions

Width

259 mm

Height

241 mm (417 mm with cover raised)

Depth

526 mm

Weight

9.7 kg (excl. accessories)

6.1 Scope of delivery

757 VA Computrace – Hardware

61

6 Appendix

Subject to changes!
All dimensions are given in mm.

6.1 Scope of delivery

6.1.1 2.757.0110 VA Computrace

The 2.757.0110 VA Computrace System includes the following accessories:

Quant. Order No. Description

1 1.757.0010 757 VA Computrace Stand

Instrument without accessories

1 6.0343.000 Pt Auxiliary electrode

1 6.0728.020 Ag/AgCl reference system

with ceramic diaphragm

Ag/AgCl/c(KCl) = 3 mol/L

Together with the 6.1245.010 Electrolyte
vessel forms a complete reference
electrode (double-junction construction,
assembly, see section 3.5.2).

The Ag/AgCl reference system is
supplied with a screwed-on holder filled
with c(KCl) = 3 mol/L.

1 6.1204.090 Stirrer tip (PTFE)

Together with the 6.1246.010
Drive shaft forms the stirrer.

116

11

116

11

∅7

58

M3

6 Appendix

757 VA Computrace – Hardware

62

Quant. Order No. Description

1 6.1226.030 Glass capillaries

for 6.1246.020 Multi-mode
electrode

Set of 10 incl. two 4.420.2800
sealing rings

1 6.1244.020 Drive belt

made of EPDM (ethylene propylene rubber), set of 3

Connection motor – drive shaft (6.1246.010 or

6.1246.000)

1 6.1245.010 Electrolyte vessel

with ceramic diaphragm

Together with the 6.0728.020
Ag/AgCl reference system forms a
complete reference electrode
(double-junction construction,
assembly, see section 3.5.2).

1 6.1246.010 Drive shaft

for stirrer incl. 2 O-rings FPM
(Viton)

Together with the 6.1204.090 stirrer
tip forms a complete stirrer.

1 6.1246.020 Multi-mode electrode

incl. 2 O-rings NBR (nitril rubber)

Together with the 6.1226.030 glass
capillary forms a complete working
electrode.

1 6.1247.020 Sealing needle

for 6.1246.020 Multi-mode
electrode

Set of 3

116

82

∅5

15

B-NS
14/15

14

46

78

70

44

6.1 Scope of delivery

757 VA Computrace – Hardware

63

Quant. Order No. Description

1 6.1415.210 Measuring vessel

clear glass

Volume: 10 ... 90 mL

7 6.1446.040 Dummy stopper

made of PVDF, with M6 thread

For closing the unused
openings in the measuring
vessel upper half

1 6.1801.080 PVC tubing

for supply of the inert gas

Length L = 4 m

4 6.1808.000 Tubing coupling

made of ETFE, with 2 M6 threads

For the connection of 2 lengths of
tubing with thread M6 (e.g.

6.1805.XXX)

1 6.1817.000 Filling tubing, made of PVC

incl. 4.420.2860 Filling cone and

6.1809.000 Tubing coupling

For filling the MME with mercury.

1 6.1824.000 4-way microtip

made of PTFE

With 4 lengths of PTFE tubing with
connection nipples with thread M6 for
the attachment of 4 765 Dosimats.

1 6.2122.0X0 Mains cable

to customer's specifications:

Cable socket

Cable plug

Type IEC 320/C 13 Type SEV 12 (CH…) ............................ 6.2122.020

Type IEC 320/C 13 Type CEE (7), VII (D…)........................6.2122.040

Type CEE (22), V Type NEMA 5-15 (USA…) ...................6.2122.070

1 6.2135.010 Connection cable to VA Com-

putrace Interface

Connection cable VA Computrace
Interface – 757 VA Computrace
Stand.

∅23

80

∅78

21.5

∅4.9

7

4

25

∅10

M6

520

100

700

2 m

6 Appendix

757 VA Computrace – Hardware

64

Quant. Order No. Description

1 6.2301.100 Lead standard solution

ρ

(Pb2+) = 1.000 ± 0.003 g/L

plastic bottle, volume V = 50 mL

To perform the test methods.

1 6.2308.020 KCl electrolyte solution

c(KCl) = 3 mol/L plastic bottle, volume V = 250 mL

For 6.0728.020/6.1245.010 Ag/AgCl reference electrode

1 6.2406.000 Mercury drop catcher

silver wire in plastic bottle

For the destruction of mercury
drops by amalgamation

1 6.2615.030 Electrode holder

For filling and storing the

6.1246.020 Multi-mode electrode

1 6.2703.000 Stand ring made of PVC

To hold the 6.1415.210
measuring vessel outside the
757 VA Computrace Stand

1 6.2709.080 Stopper

For closing the pipetting
aperture of the 757 VA
Computrace Stand

1 6.2711.030 Drip pan

made of PS (polystyrene)

For filling the Multi-mode
electrode with mercury

100

∅32

52

80

∅63

50

∅53.2

18

76

290

210

60

6.1 Scope of delivery

757 VA Computrace – Hardware

65

Quant. Order No. Description

1 6.2711.040 Drip pan

made of PS (polystyrene)

To be inserted in the 757 VA
Computrace Stand

1 6.2730.030 Stopper

with nipple and O-ring

For closing the opening of the
757 VA Computrace Stand
when the 6.1824.000 4-way
microtip is not used (inserted in
opening 59)

1 6.2739.000 Spanner

for screwing down plastic
nipples

1 6.2816.020 Syringe

made of PP, with Luer connec­tion

Volume V = 10 mL

For filling the MME

1 6.2816.030 Needle

for 6.2816.020 syringe

1 6.5326.000 VA Computrace Interface cpl.

For connection of VA Computrace Stand 757 to PC via USB
incl. the following accessories:

1 × 6.2155.000 VA Computrace Interface
1 × 6.2151.020 USB Cable 1.8 m
1 × 6.2158.000 Mains adapter 100...240V/5V DC

1 6.6032.100 PC Software CD «VA Computrace 2.0»

1 8.757.1013 Hardware Manuel (English)

Instructions for Use for 757 VA Computrace Stand

1 8.757.1027 Registration card (German/English)

for PC program «757 VA Computrace 2.0»

1 8.757.2003 "VA Application Notes" (English)

1 8.757.5003 Metrohm Monograph "Practical voltammetry" (English)

1 8.757.8023 Software Manual (English)

Instructions for Use for PC program «757 VA Computrace 2.0»

150

20

200

38

∅10

∅8

68

102

80

∅0.8

6 Appendix

757 VA Computrace – Hardware

66

6.1.2 2.757.0120 VA Computrace

The 2.757.0120 VA Computrace System includes the following accessories:

Quant. Order No. Description

1 1.757.0010 757 VA Computrace Stand

Instrument without accessories

7 6.1446.040 Dummy stopper

made of PVDF, with M6 thread

For closing the unused
openings in the measuring
vessel upper half

1 6.1801.080 PVC tubing

for supply of the inert gas

Length L = 4 m

4 6.1808.000 Tubing coupling

made of ETFE, with 2 M6 threads

For the connection of 2 lengths of
tubing with thread M6 (e.g.

6.1805.XXX)

1 6.1824.000 4-way microtip

made of PTFE

With 4 lengths of PTFE tubing with
connection nipples with thread M6 for
the attachment of 4 765 Dosimats.

1 6.2122.0X0 Mains cable

to customer's specifications:

Cable socket

Cable plug

Type IEC 320/C 13 Type SEV 12 (CH…)............................ 6.2122.020

Type IEC 320/C 13 Type CEE (7), VII (D…) ....................... 6.2122.040

Type CEE (22), V Type NEMA 5-15 (USA…)................... 6.2122.070

1 6.2135.010 Connection cable to VA Com-

putrace Interface

Connection cable VA Computrace
Interface – 757 VA Computrace
Stand.

1 6.2301.100 Lead standard solution

ρ

(Pb2+) = 1.000 ± 0.003 g/L

plastic bottle, volume V = 50 mL

To perform the test methods.

1 6.2308.020 KCl electrolyte solution

c(KCl) = 3 mol/L plastic bottle, volume V = 250 mL

For 6.0728.020/6.1245.010 Ag/AgCl reference electrode

21.5

∅4.9

7

4

25

∅10

M6

100

700

2 m

6.1 Scope of delivery

757 VA Computrace – Hardware

67

Quant. Order No. Description

1 6.2709.080 Stopper

For closing the pipetting
aperture of the 757 VA
Computrace Stand

1 6.2711.040 Drip pan

made of PS (polystyrene)

To be inserted in the 757 VA
Computrace Stand

1 6.2730.030 Stopper

with nipple and O-ring

For closing the opening of the
757 VA Computrace Stand
when the 6.1824.000 4-way
microtip is not used (inserted in
opening 59)

1 6.2739.000 Spanner

for screwing down plastic
nipples

1 6.5326.000 VA Computrace Interface kpl.

For connection of VA Computrace Stand 757 to PC via USB

incl. the following accessories:
1 × 6.2155.000 VA Computrace Interface

1 × 6.2151.020 USB Cable 1.8 m
1 × 6.2158.000 Mains adapter 100...240V/5V DC

1 6.6032.100 PC Software CD «VA Computrace 2.0»

1 8.757.1013 Hardware Manuel (English)

Instructions for Use for 757 VA Computrace Stand

1 8.757.1027 Registration card (German/English)

for PC program «757 VA Computrace 2.0»

1 8.757.2003 "VA Application Notes" (English)

1 8.757.5003 Metrohm Monograph "Practical voltammetry" (English)

1 8.757.8023 Software Manual (English)

Instructions for Use for PC program «757 VA Computrace 2.0»

18

76

150

20

200

38

∅10

∅8

68

6 Appendix

757 VA Computrace – Hardware

68

6.2 Options

Order No. Description

6.0728.010 Ag/AgCl reference system

with ceramic diaphragm

Together with the 6.1245.010 Electrolyte
vessel forms a complete reference
electrode (double-junction construction,
assembly, see section 3.5.2).

The Ag/AgCl reference system is
supplied with an empty holder screwed
on; the holder can be filled with the
desired reference electrolyte.

6.1204.XXX Electrode tip

Together with the 6.1246.000 Drive shaft forms the
stirrer. The following electrode tips are available:

Order No. Disk material Shaft material

6.1204.100 Ultra Trace Graphite PVC

6.1204.110 Glassy Carbon (GC) PEEK

6.1204.120 Pt PEEK

6.1204.130 Ag PEEK

6.1204.140 Au PEEK

6.1204.150 Au PEEK

Disk diameter: 2.0 +0 / –0.05 mm

Concentricity error: ≤ 0.2 mm

6.1241.020 Electrode holder

to take the 6.1247.000 glassy carbon rod

Together with the 6.1247.000 glassy carbon rod
forms the GC auxiliary electrode.

6.1246.000 Drive shaft for rotating disk electrode

incl. 2 O-rings FPM (Viton)

Together with the 6.1204.XXX electrode tips
forms the rotating disk electrode (RDE).

11

14

65

52.5

∅2.1

∅7

M3

116

46

6.2 Options

757 VA Computrace – Hardware

69

Order No. Description

6.1247.000 Glassy carbon tip

Together with the 6.1241.020
electrode holder forms the GC
auxiliary electrode.

6.1247.040 Slotted screw

Slotted screw 75 with holding
sleeve.

6.1415.150 Measuring vessel

clear glass, incl. 6.2036.000
holding ring

Volume: 5 ... 70 mL

6.1418.220 Measuring vessel

clear glass, with thermostatic jacket;
incl. 6.2036.000 holding ring

Volume: 12 ... 70 mL

6.1450.210 Measuring vessel

Made of PFA (polyfluoralkyloxy­copolymer), incl. 2036.000 holding
ring

Volume: 10 ... 90 mL

6.2709.040 Stopper

made of PVC, incl. 2 E.301.0004 O-rings of
NBR (nitril rubber)

For closing the MME opening when the RDE
is used; with two dummy holes (thread M6)
for holding the two MME gas lines not used
in operation with the RDE.

6.2802.000 Polishing kit

for mechanical regeneration of the active surface of 6.1204.XXX
electrode tips

comprising: 1 × 2 g α-Al

2O3

(0.3 µm)

1 × polishing cloth

∅78

68

∅23

∅30

∅78

∅78

80

65

∅2

82

80

20

33

∅23

6 Appendix

757 VA Computrace – Hardware

70

Order No. Description

6.2827.000 Trimming tool

for regeneration of the 6.1204.100 Ultra Trace
Graphite electrode

2.765.0010 765 Dosimat

Dispensing unit for 757 VA Computrace Stand.

6.3014.XXX Exchange unit

with standard reagent bottle of brown glass, rectangular, volume V = 1 L, with
GL 45 ISO/DIN glass thread; burette cylinder of clear glass with light protector;
PCTFE/PTFE flat stopcock

6.3014.153 burette volume V = 5 mL

6.3014.213 burette volume V = 10 mL

6.3014.223 burette volume V = 20 mL

6.3014.253 burette volume V = 50 mL

6.2141.080 Connecting cable for 765 Dosimats

Connecting cable 2 × 765 Dosimat – 757 VA Computrace Stand.

6.9921.170 Connecting cable for 765 Dosimats

Connecting cable 5 × 765 Dosimat – 757 VA Computrace Stand.

2.813.0020 813 Compact Autosampler for VA applications
Sample changer for up to 18 sample vessels

2.731.0010 731 Relay Box

Control unit for the two 772 Pump Units needed for operation of the 813
Compact Autosampler

2.772.0010 772 Pump Unit
Peristaltic pump for operation of 813 Compact Autosampler

6.2141.150 Connecting cable 757–731–813

Cable for connection of 731 Relay Box and 813 Compact Autosampler to 757 VA
Computrace Stand

6.5323.010 Rinsing equipment for VA Computrace 757

incl. the following accessories:

1 × 6.1456.210 Measuring vessel for sample changer operation
2 × 6.1602.105 Siphon GL45
2 × 6.1618.050 Thread adapter 40 mm/GL45
2 × 6.1621.000 PE container, V = 10 L
1 × 6.1805.020 FEP tubing, L = 52 cm
1 × 6.1805.100 FEP tubing, L = 40 cm
1 × 6.1805.180 FEP tubing, L = 16 cm
4 × 6.1805.530 FEP tubing, L = 200 cm
1 × 6.1808.000 Coupling bush, with 2 threads M6
2 × 6.1819.010 PTFE tube, L = 86 mm
1 × 6.1819.020 FEP tube, L = 250 cm
4 × 6.1820.020 Screw connector
1 × 6.1829.020 FEP aspiration tubing, L = 500 cm

49

53

6.3 Warranty

757 VA Computrace – Hardware

71

6.3 Warranty

The warranty on our products is limited to defects that are traceable to material,
construction or manufacturing error, which occur within 12 months from the day of
delivery. In this case, the defects will be rectified in our workshops free of charge.
Transport costs are to be paid by the customer.

For day and night operation, the warranty is limited to 6 months.

Glass breakage in the case of electrodes or other parts is not covered by the war­ranty. Checks, which are not a result of material or manufacturing faults, are also
charged during the warranty period. For parts of outside manufacture insofar as
these constitute an appreciable part of our instrument, the warranty stipulations of
the manufacturer in question apply.

With the regard to the guarantee of accuracy, the technical specifications in the in­struction manual are authoritative.

Concerning defects in material, construction or design as well as the absence of
guaranteed features, the orderer has no rights or claims except those mentioned
above.

If damage of the packaging is evident on receipt of a consignment or if the goods
show signs of transport damage after unpacking, the carrier must be informed im­mediately and a written damage report demanded. lack of an official damage report
releases Metrohm from any liability to pay compensation.

If any instruments and parts have to be returned, the original packaging should be
used if at all possible. This applies above all to instruments, electrodes, burette cyl­inders and PTFE pistons. Before embedment in wood shavings or similar material,
the parts must be packed in a dustproof package (for instruments, use of a plastic
bag is imperative). If open assemblies are enclosed in the scope of delivery that are
sensitive to electromagnetic voltages (e.g. data interfaces etc.) these must be re­turned in the associated original protective packaging (e.g. conductive protective
bag). (Exception: assemblies with built-in voltage source belong in a non­conductive protective packaging). For damage that arises as a result of non­compliance with these instructions, no warranty responsibility whatsoever will be
accepted by Metrohm.

6 Appendix

757 VA Computrace – Hardware

72

6.4 EU Declaration of conformity

EU Declaration of Conformity

The METROHM AG company, Herisau, Switzerland hereby certifies, that the in­strument:

757 VA Computrace

meets the requirements of EC Directives 89/336/EWG and 73/23/EWG.

Source of the specifications:

EN 50081 Electromagnetic compatibility, basic specification

Emitted Interference

EN 50082 Electromagnetic compatibility, basic specification

Interference Immunity

EN 61010 Safety requirements for electrical equipment for measure-

ment, control and laboratory use

Description of the instrument:

PC-controlled system for polarographic and voltammetric trace analysis of

organic and inorganic substances.

Herisau, April 28, 1998

Dr. J. Frank Ch. Buchmann

Development Manager Production and
Quality Assurance Manager

6.5 Certificate of conformity and system validation

757 VA Computrace – Hardware

73

6.5 Certificate of conformity and
system validation

Certificate of Conformity and System Validation

This is to certify the conformity to the standard specifications for electrical appli­ances and accessories, as well as to the standard specifications for security and
to system validation issued by the manufacturing company.

Name of commodity:

757 VA Computrace

Name of manufacturer: Metrohm Ltd., Herisau, Switzerland

Principal technical information: Voltage: 100…240 V
Frequency: 50…60 Hz
Power consumption: 26 W

This Metrohm instrument has been built and has undergone final type testing
according to the standards:

IEC61000-4-2 (level 4), IEC61000-4-3 (level 2), IEC61000-4-4 (level 4),
IEC61000-4-5 (level 2/3), IEC61000-4-6 (level 3), IEC61000-4-8,
IEC61000-4-11, ENV50204, EN55022 (class B), EN50081-1/2, EN50082-1/2

— Electromagnetic compatibility

IEC61010, EN61010, UL3101-1

— Security specifications

The technical specifications are documented in the instruction manual.

Metrohm Ltd. is holder of the SQS-certificate of the quality system ISO 9001 for
quality assurance in design/development, production, installation and servicing.

Herisau, April 28, 1998

Dr. J. Frank Ch. Buchmann

Development Manager Production and
Quality Assurance Manager

6 Appendix

757 VA Computrace – Hardware

74

6.6 Index

A

Ag electrode tip (6.1204.130) ................................34,68

Ag/AgCl filling 105

Figure ......................................................................36

Ag/AgCl reference system.......... see Reference system

Ambient temperature..................................................60

Appendix.....................................................................61

Application Bulletins .....................................................4

Application Notes .........................................................6

Au electrode tip (6.1204.140) ................................34,68

Au electrode tip (6.1204.150) ................................34,68

Auxiliary electrode 39

Construction............................................................38

Electrical connection...............................................38

Figure ............................................................11,35,39

Insertion in measuring head ..............................18,38

Installation ...............................................................38

Startup procedure ...................................................38

Technical data.........................................................59

B

Bridging electrolyte..................................................... 37

C

Cable (6.2135.010)

Figure ......................................................................15

Installation ...............................................................15

Ordering designation ......................................... 63,66

Cable (6.2141.080)

Connection of Dosimats .........................................40

Figure ......................................................................44

Ordering designation .............................................. 70

Cable (6.2141.150)

Figure ......................................................................44

Ordering designation .............................................. 70

Cable (6.2151.020)

Figure ......................................................................15

Installation ...............................................................15

Ordering designation ......................................... 65,67

Cable (6.9921.170)

Connection of Dosimats .........................................40

Ordering designation .............................................. 70

Capillary............................................see Glass capillary

Caution .........................................................................3

Certificate of conformity and system validation .........73

Changing capillary...................................................... 31

Changing Exchange unit ............................................ 41

Check of instrument ...................................................13

Cleaning the MME ......................................................32

Collecting mercury......................................................53

Comment......................................................................3

Compact Autosampler 813

Electrical connection...............................................43

Operation ................................................................50

Ordering designation .............................................. 70

Tubing connections ................................................46

Conformity .............................................................72,73

Connection 10 for inert gas supply

Figure ........................................................................9

Inert gas supply ......................................................19

Connection 14

Connection of the VA Computrace Interfaces........ 15

Figure........................................................................ 9

Connection 15

Connection of 813 Compact Autosampler............. 43

Connection of Dosimat 765.................................... 40

Figure........................................................................ 9

Connection 72 for inert gas supply

Attachment of FEP tubing 30 ................................. 18

Figure...................................................................... 22

Inert gas connection scheme ................................. 20

Connection 73 for inert gas supply

Attachment of FEP tubing 38 ................................. 18

Figure...................................................................... 22

Inert gas connection scheme ................................. 20

Connection 8 for inert gas lead-off

Figure........................................................................ 9

Connection 9 for waste solution lead-off

Figure........................................................................ 9

Connection of 765 Dosimats ..................................... 40

Connection of the 813 Compact Autosampler .......... 43

Connection to the PC................................................. 15

Contact pin 81

Figure...................................................................... 22

Cover 1 of measuring head arm

Figure........................................................................ 8

Current measurement ................................................58

D

Deaeration of analyte solution.................................... 19

Declaration of conformity ........................................... 72

Depth.......................................................................... 60

Diaphragm 108

Figure...................................................................... 36

Diaphragm 111

Figure...................................................................... 36

Diaphragm support 107

Figure...................................................................... 36

Dimensions ................................................................ 60

Dispose of mercury.................................................... 54

DME............................................................................ 21

Dosimat 765

Addition of standard solutions................................ 40

Connecting cable ................................................... 70

Electrical connection .............................................. 40

Exchange units ....................................................... 40

Ordering designation.............................................. 70

Tubing connections ................................................ 40

Drip pan 7 (6.2711.040)

Figure........................................................................ 8

Ordering designation......................................... 65,67

Setting up ............................................................... 13

Drip pan 92 (6.2711.030)

Figure................................................................. 23,27

Ordering designation.............................................. 64

Drive belt 28 (6.1244.020)

Figure................................................................. 11,35

Installation.......................................................... 16,39

Ordering designation.............................................. 62

Drive shaft 24 (6.1246.010)

Figure...................................................................... 11

Insertion in measuring head ................................... 16

Installation............................................................... 39

6.6 Index

757 VA Computrace – Hardware

75

Installing the drive belt ............................................16

Ordering designation ..............................................62

Drive shaft 100 (6.1246.000)

Construction of RDE ...............................................34

Figure ......................................................................35

Insertion in measuring head....................................16

Ordering designation ..............................................68

Drive wheel 31

Figure .................................................................11,35

Installing the drive belt 28 ..................................16,39

Dummy cell .................................................................59

Dummy cell connection 46.........................................12

Dummy cell connection 47.........................................12

Dummy cell connection 48.........................................12

Dummy cell connection 49.........................................12

Dummy stopper 21 (6.1446.040)

Figure ......................................................................11

Ordering designation .........................................63,66

Dummy stopper 40 (6.1446.040)

Figure ......................................................................11

Insertion in measuring head....................................16

Ordering designation .........................................63,66

Dummy stopper 41 (6.1446.040)

Figure ......................................................................11

Insertion in measuring head....................................16

Ordering designation .........................................63,66

E

Electrical connection 103

Figure ......................................................................36

Electrical connection 112

Figure ......................................................................39

Electrical safety...........................................................51

Electrode cable 16 (WE)

Connection to MME ................................................18

Connection to RDE .................................................16

Figure .................................................................11,35

Electrode cable 27 (RE)

Attachment to reference electrode..........................37

Connection to reference electrode..........................18

Figure ......................................................................11

Electrode cable 37 (AE)

Attachment to auxiliary electrode............................38

Connection to auxiliary electrode............................18

Figure .................................................................11,35

Electrode holder 93 (6.2615.030)

Figure .................................................................23,27

Ordering designation ..............................................64

Electrode holder 115 (6.1241.020)

Figure ......................................................................39

Ordering designation ..............................................68

Electrode tip 99 (6.1204.XXX)

Construction of RDE ...............................................34

Figure ......................................................................35

Insertion in measuring head....................................16

Ordering designation ..............................................68

Regeneration...........................................................34

Electrolyte compartement 106

Figure ......................................................................36

Electrolyte compartement 110

Figure ......................................................................36

Electrolyte vessel 102 (6.1245.010)

Figure ......................................................................36

Ordering designation ..............................................62

Electromagnetic compatibility ....................................60

EMC ............................................................................60

Emitted interference....................................................60

Equipping the measuring head.................................. 16

EU Declaration of conformity .....................................72

Exchange unit (6.3014.XXX)

Changing the exchange unit................................... 41

Choice of exchange unit ......................................... 40

Ordering designation.............................................. 70

F

FEP tubing 18 (6.1805.180)

Figure......................................................................11

FEP tubing 30 (6.1805.180)

Connection to MME ................................................ 18

Connection to stopper 98....................................... 18

Figure.................................................................11,35

FEP tubing 32 (6.1805.040)

Figure......................................................................11

FEP tubing 34 (6.1805.100)

Figure.................................................................11,45

FEP tubing 35 (6.1805.090)

Figure.................................................................11,35

FEP tubing 36 (6.1805.180)

Figure.................................................................11,35

FEP tubing 38 (6.1805.180)

Connection to MME ................................................ 18

Connection to stopper 98....................................... 18

Figure.................................................................11,35

FEP tubing 118 (6.1805.180)

Figure......................................................................45

Installation...............................................................46

FEP tubing 119 (6.1805.100)

Figure......................................................................45

Installation...............................................................46

Filling capillary using vacuum ....................................26

Filling capillary without vacuum.................................. 24

Filling cone 95 (4.420.2860)

Figure......................................................................27

Filling station ..............................................................27

Filling the MME with mercury .....................................23

Filling tubing 94 (6.1817.000)

Figure......................................................................27

Ordering designation.............................................. 63

Front .............................................................................8

G

Gas wash bottle 4 (6.2405.030)

Figure...................................................................8,11

Filling with water...................................................... 19

Inert gas connection scheme .................................20

Gas wash bottle 44 (6.2405.030)

Figure.................................................................12,45

Gas wash bottle 96

Figure......................................................................27

GC electrode tip (6.1204.110)...............................34,68

Glass breakage .......................................................... 71

Glass capillary 88 (6.1226.030)

Figure.................................................................22,27

Filling with vacuum .................................................26

Filling without vacuum ............................................24

Mounting the capillary............................................. 24

Ordering designation.............................................. 62

Replacement........................................................... 31

Glassy carbon tip 117 (6.1247.000)

Figure......................................................................39

Ordering designation.............................................. 69

Graphite electrode tip (6.1204.100) ......................34,68

6 Appendix

757 VA Computrace – Hardware

76

H

Handling of mercury ...................................................53

Hazard ..........................................................................3

Height .........................................................................60

HMDE .........................................................................21

Holder 3 for measuring vessel

Figure ........................................................................8

Installation of measuring vessel..............................18

I

Immunity to interference .............................................60

Inert gas...................................................................... 59

Inert gas connection...................................................19

Inert gas lead-off.........................................................19

Inert gas pressure.......................................................19

Inert gas supply ..........................................................19

Information about the Instructions for Use...................2

Input bias current........................................................57

Input impedance.........................................................57

Insert ring 84 (4.420.3011)

Figure ......................................................................22

Installation...................................................................13

Instrument description..................................................1

Internal electrolyte.......................................................37

Introduction...................................................................1

K

KCl electrolyte solution (6.2308.020).....................64,66

L

Lead standard solution (6.2301.100) ....................64,66

Left side view ..............................................................10

Location of instrument................................................13

Locking ring 74 (4.420.2920)

Figure ......................................................................22

Locking ring 86 (4.420.2870)

Figure ......................................................................22

Locking ring 116

Figure ......................................................................39

M

Mains Adapter (6.2158.000)

Figure ......................................................................15

Installation ...............................................................15

Ordering designation ......................................... 65,67

Mains cable ......................................................14,63,66

Mains connection .............................................14,51,60

Mains connection plug 13

Figure ........................................................................9

Mains connection.................................................... 14

Mains frequency ......................................................... 60

Mains pilot lamp 5

Figure ........................................................................8

Function ..................................................................14

Mains switch 12

Figure ........................................................................9

Switch instrument on/off .........................................14

Mains voltage

Technical data.........................................................60

Material of base ..........................................................60

Material of cover......................................................... 60

Material of measuring arm .........................................60

Measurement techniques........................................... 57

Measuring head 20

Equipping ............................................................... 16

Figure....................................................... 11,17,35,45

Measuring head arm 19

Figure....................................................... 11,17,35,45

Measuring vessel 6 (6.1415.210)

Figure........................................................................ 8

Installation............................................................... 18

Ordering designation.............................................. 63

Measuring vessel (6.1415.150).................................. 69

Measuring vessel (6.1418.220).................................. 69

Measuring vessel (6.1450.210).................................. 69

Measuring vessels ..................................................... 59

Mercury

Filling capillary with vacuum................................... 26

Filling capillary without vacuum.............................. 24

Filling with mercury ................................................. 23

Handling ................................................................. 53

Properties ............................................................... 52

References.............................................................. 55

Replenishing ........................................................... 30

Safety considerations ............................................. 52

Threshold limit value (TLV) ..................................... 52

Toxicity.................................................................... 53

Mercury drop catcher (6.2406.000) ........................... 64

Mercury electrodes..................................................... 21

Mercury reservoir 82

Figure...................................................................... 22

Filling with mercury ................................................. 23

Replenishing the mercury....................................... 30

Microtip 26 (6.1824.000)

Connection to 765 Dosimat.................................... 40

Figure...................................................................... 11

Insertion in measuring head ................................... 16

Ordering designation......................................... 63,66

MME ...................................... see Multi-mode electrode

Monographs................................................................. 6

Multi-mode electrode 17

Changing capillary.................................................. 31

Cleaning.................................................................. 32

Construction ...........................................................21

Electrical connection .............................................. 28

Figure....................................................... 11,22,23,27

Filling capillary with vacuum................................... 26

Filling capillary without vacuum.............................. 25

Filling with mercury ................................................. 23

Insertion in measuring head .............................. 18,28

Mounting capillary .................................................. 24

Operating characteristics ....................................... 21

Ordering designation.............................................. 62

Replenishing mercury............................................. 30

Storage ...................................................................30

Technical data ........................................................58

N

Needle 91 (6.2816.030)

Figure...................................................................... 23

Ordering designation.............................................. 65

Nipple 23 (6.2730.030)

Figure...................................................................... 11

Nitrogen................................................................. 19,59

Noise .......................................................................... 57

Notation........................................................................ 3

6.6 Index

757 VA Computrace – Hardware

77

O

Opening 51

Figure ......................................................................17

Insertion of auxiliary electrode............................18,38

Opening 52

Insertion of stopper 41............................................16

Opening 53

Insertion of stopper 40............................................16

Opening 55

Figure ......................................................................17

Inserting stopper 98................................................18

Inserting the MME ...................................................18

Opening 58

Figure ......................................................................17

Insertion of reference electrode .........................18,37

Opening 60

Figure ......................................................................17

Insertion of RDE ......................................................16

Insertion of stirrer................................................16,39

Opening 65

Figure ......................................................................17

Insertion of PTFE tubing..........................................16

Opening the instrument ..............................................51

Options .......................................................................68

Output current.............................................................57

Output voltage ............................................................57

P

Packaging...................................................................13

Parts and controls.........................................................7

Pictograms....................................................................3

Pipetting needle (6.1835.030).....................................46

Pipetting opening 54

Figure ......................................................................17

Polishing kit (6.2802.000) ...........................................69

Potentiostat.................................................................57

Power consumption....................................................60

Properties of mercury .................................................52

Protection against static charges ...............................51

Protection class .....................................................51,60

Pt Auxiliary electrode 113 (6.0343.000)

Figure ......................................................................39

Ordering designation ..............................................61

Pt electrode tip (6.1204.120) .................................34,68

Pt tip 114

Figure ......................................................................39

PTFE tube 25 (6.1819.000)

Figure ......................................................................11

PTFE tube 29 (4.647.1350)

Figure ......................................................................11

PTFE tube 43 (6.1819.010)

Figure .................................................................12,45

Installation ...............................................................46

PTFE tube 45 (6.1819.010)

Figure .................................................................12,45

Installation ...............................................................46

PTFE tube 120 (6.1819.010)

Figure ......................................................................45

Installation ...............................................................46

PTFE tube 121 (6.1819.010)

Figure ......................................................................45

Installation ...............................................................46

Pulse amplitude ..........................................................58

Pump Unit 772

Electrical connection ...............................................43

Ordering designation.............................................. 70

Tubing connections ................................................ 46

PVC tubing (6.1801.080) .................................. 19,63,66

R

RDE

Construction ...........................................................34

Figure......................................................................35

Insertion in measuring head ................................... 16

Regeneration ..........................................................34

Startup procedure................................................... 34

Technical data ........................................................58

Rear .............................................................................. 9

Reference electrode 22

Add bridging electrolyte.......................................... 37

Add internal electrolyte ...........................................37

Construction ...........................................................36

Electrical connection............................................... 37

Figure.................................................................11,36

Insertion in measuring head .............................. 18,37

Installation...............................................................37

Startup procedure................................................... 37

Technical data ........................................................58

Reference system 101 (6.0728.0X0)

Figure......................................................................36

Ordering designation......................................... 61,68

References dealing with mercury............................... 55

Regeneration of RDE.................................................. 34

Relay Box 731

Electrical connection............................................... 43

Ordering designation.............................................. 70

Tubing connections ................................................ 46

Replenishing mercury................................................. 30

Reprints ........................................................................6

Retaining nut 87 (4.420.2850)

Figure......................................................................22

Mounting the capillary............................................. 24

Right side view ...........................................................10

Rinsing equipment (6.5323.010)

Ordering designation.............................................. 70

S

Safety.......................................................................... 51

Safety considerations concerning mercury................ 52

Safety directions.........................................................60

Safety specifications ..................................................60

Scheme of inert gas connections............................... 20

Screw connection 89

Connection of electrode cable 16 ..........................18

Figure......................................................................22

Screw thread 77

Figure......................................................................22

Screw thread 79

Figure......................................................................22

Screw thread 83

Figure......................................................................22

Sealing needle 76 (6.1247.020)

Adjusting............................................................ 25,29

Figure......................................................................22

Operating characteristics........................................ 21

Ordering designation.............................................. 62

Replacement........................................................... 33

Sealing ring 85 (4.420.2800)

Figure......................................................................22

Replacement........................................................... 33

6 Appendix

757 VA Computrace – Hardware

78

Serial number 11

Figure ........................................................................9

Setting up filling station ..............................................27

Setting up instrument .................................................13

Slotted screw 33

Figure ......................................................................11

Inert gas connection scheme .................................20

Slotted screw 50

Figure ......................................................................12

Inert gas connection scheme .................................20

Slotted screw 75 (6.1247.040)

Adjusting the mercury flow.................................25,29

Figure ......................................................................22

Ordering designation .............................................. 69

Slotted screw 80 (4.420.2960)

Figure ......................................................................22

SMDE..........................................................................21

Software installation....................................................15

Software Manual...........................................................1

Software settings ........................................................48

Spanner (6.2739.000)............................................65,67

Stand ring (6.2703.000)..............................................64

Static charges............................................................. 51

Stirrer

Construction............................................................39

Insertion in measuring head ..............................16,39

Startup procedure ...................................................39

Technical data.........................................................59

Stirrer tip 42 (6.1204.090)

Figure ......................................................................11

Insertion in measuring head ...................................16

Installation ...............................................................39

Ordering designation .............................................. 61

Stopper 2 (6.2709.080)

Figure ..............................................................8,11,35

Ordering designation ......................................... 64,67

Stopper 98 (6.2709.040)

Connection of FEP tubing 30..................................18

Connection of FEP tubing 38..................................18

Figure ......................................................................35

Insertion in measuring head ...................................18

Ordering designation .............................................. 69

Stopper (6.2730.030).............................................65,67

Storage temperature...................................................60

Storing the MME .........................................................30

Support documentation................................................4

Sweep rate..................................................................58

Sweep voltage range.................................................. 57

Switch off instrument .................................................. 14

Switch on instrument ..................................................14

Syringe 90 (6.2816.020)

Figure ......................................................................23

Filling with mercury .................................................24

Ordering designation .............................................. 65

System validation........................................................73

T

Technical data ............................................................57

Threaded opening 52

Figure ......................................................................17

Threaded opening 53

Figure ......................................................................17

Threaded opening 56

Figure...................................................................... 17

Threaded opening 57

Figure...................................................................... 17

Threaded opening 59

Figure...................................................................... 17

Threaded opening 61

Figure...................................................................... 17

Threaded opening 62

Figure...................................................................... 17

Threaded opening 63

Figure...................................................................... 17

Threaded opening 64

Figure...................................................................... 17

Threaded opening 66

Figure...................................................................... 18

Threaded opening 67

Figure...................................................................... 18

Toxicity of mercury .....................................................53

Transfer tubing (6.1822.410)...................................... 46

Transport damage................................................. 13,71

Transport temperature ............................................... 60

Trapping of mercury drops ........................................ 54

Trimming tool (6.2827.000) ........................................ 70

Tubing coupling 118 (6.1809.000)

Figure...................................................................... 27

Tubing coupling (6.1808.000) ............................... 63,66

U

Ultra Trace graphite electrode tip (6.1204.100) .... 34,68

V

VA Computrace Interface

Data transfer ............................................................. 1

Figure...................................................................... 15

Installation............................................................... 15

Ordering designation......................................... 65,67

Technical data ........................................................60

VA Computrace Stand

Certificate of conformity and system validation ..... 73

Connection to the PC .............................................15

EU declaration of conformity .................................. 72

Inert gas connection............................................... 19

Installation............................................................... 14

Options ................................................................... 68

Scope of delivery ............................................... 61,66

Vacuum pump............................................................ 26

Valves ......................................................................... 20

Vent opening 104

Figure...................................................................... 36

Vent opening 109

Figure...................................................................... 36

Voltage resolution....................................................... 57

W

Warning ........................................................................ 3

Warranty ..................................................................... 71

Weight ........................................................................60