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 info@metrohm.ch
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.
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