MARKES UNITY Thermal Desorber USER MANUAL
UUNNIITTYY
Thermal
Desorber
USER MANUAL
SEPTEMBER 2006
QUI-0002
V
ERSION 5.2
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QUI-0002 vs 5.2 September 2006
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1 Warnings and disclaimers 8
1.1 Electricity 8
1.2 Compressed gases 8
1.3 Hydrogen gas 8
2 UNITY Preinstallation Check List 8
2.1 Minimum computer specification for UNITY control 8
2.2 GC equipment requirements 8
2.3 Access into the GC oven 8
2.4 GC configuration/parameter selection 8
2.5 Laboratory location 9
2.5.1 Space requirements 9
2.5.2 Recommendations relating to the quality of the laboratory air 9
2.5.3 Recommendations relating to the quality of the laboratory gas lines 9
2.6 Services 9
2.6.1 Power 9
2.6.2 Pressure controlled air supply 9
2.6.2.1 Functions 9
2.6.2.2 Specification required (dryness / purity) 9
2.6.2.3 Consumption 10
2.6.3 Pressure controlled carrier gas supply 10
2.6.3.1 Gas selection - type / purity 10
2.6.3.2 Line pressures and recommended pneumatic control 10
2.6.3.3 UNITY Pneumatic Control Accessories 10
2.6.3.4 Filters 10
3 System description and summary of operation 10
3.1 Parameters and ranges 10
3.2 Sample flow path and key system components 11
3.3 Operational sequence for 2(3) stage desorption mode 12
3.4 Operational sequence for tube conditioning mode 19
3.5 Sample tubes 19
3.6 Tube desorption oven 19
3.7 Tube filters and seals 19
3.8 The cold trap 19
3.9 Cold trap cooling and heating 19
3.10Gas flow through the cold trap 19
3.11 Trap filters and seals 20
3.12Split filters 20
3.13User interface 20
4 UNITY Installation 20
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4.1 Packing list 20
4.2 Installing the cold trap 22
4.2.1 Trap sorbent selection 22
4.2.2 Packing the cold trap 22
4.2.3 Cold trap installation 23
4.3 Installing the transfer line 26
4.3.1 Connecting the transfer line to the gas chromatograph 26
4.3.2 Installing the fused silica transfer line insert 28
4.3.3 Connecting the transfer line to UNITY 28
4.3.4 Coupling the fused silica transfer line to the GC analytical column 29
4.4 Cabling 30
4.4.1 Power 30
4.4.2 Connecting UNITY to the rest of the analytical system 30
4.4.3 Connecting UNITY to the PC 31
4.5 Connecting the gas supplies 31
4.5.1 Carrier gas 31
4.5.2 Air
4.6 Disconnecting / Connecting the Auxilliary heater 31
5 Switching on. 32
6 Loading the UNITY software 32
6.1 Loading UNITY software onto your PC 32
6.2 Downloading UNITY Control software from the PC to UNITY to initialise the system 32
6.3 The UNITY LED 32
7 Introduction to the principles of two-stage thermal desorption 33
7.1 Capillary cryofocusing 33
7.2 Cold trapping 33
8 Guidance on air sampling 33
8.1 Sorbent selection 33
8.1.1 Carbotrap C
TM
(20-40 mesh) / Carbopack CTM(60-80 mesh) / Carbograph 1TD
TM
34
8.1.2 Tenax TA
TM
or GR
TM
34
8.1.3 Carbotrap
TM
(20-40 mesh) / Carbopack BTM(60-80 mesh) / GCB1
TM
34
/ Carbograph 2TD
TM
8.1.4 Chromosorb 102
TM
34
8.1.5 Chromosorb 106
TM
35
8.1.6 Porapak N
TM
35
8.1.7 Porapak Q
TM
35
8.1.8 Spherocarb
TM
/ UniCarb
TM
36
8.1.9 Carbosieve SIII
TM
36
8.1.10 Carboxen 1000 36
8.1.11 Molecular Sieve 37
8.2 Packing Tubes 37
8.3 Diffusive Monitoring 37
8.3.1 Principles and Theory 37
8.3.2 Tube-type Axial Diffusive Samplers 38
8.3.3 Diffusive sampling in practice 39
8.3.4 Radial Diffusive Samplers 39
8.3.5 When diffusive sampling is not applicable 40
8.4 Pumped Air Monitoring 40
9 Guidance on Materials Testing 41
9.1 Direct Desorption of material from tubes 41
9.1.1 Solid samples 42
9.1.2 Liquids, emulsions, resins and other semi-liquid products. 42
9.2 Off-line purge and trap into sorbent tubes. 43
10 Guidance on TD / GC analytical conditions 43
10.1Occupational Hygiene 43
10.2Ambient / Indoor air 44
10.3Materials testing - residual solvents in consumer products 44
10.4High boiling components 45
11 Calibration and preparing and introducing standards 46
11.1 Calibration Method 1. - Introducing standards in the vapour phase using the 46
Calibration Solution Loading Rig
11.1.1Criteria for Method 1 47
11.2 Calibration Method 2. - introducing standards directly as liquids 47
11.2.1Criteria for Method 2 47
11.3 Calculating the expected sample mass. 48
11.3.1Diffusive air monitoring for toluene 48
11.3.2Pumped air monitoring for n-heptane 48
11.3.3Solid sampling for residual acetone 48
11.4 Quality assurance and calibration 49
11.4.1Certified Reference Standard (CRS) tubes 49
11.4.2External Quality Assessment Schemes 50
12 Insertion and removal of a sample tube in UNITY 50
12.1Insertion 50
12.2Removal 50
13 Preparing for analysis 51
13.1Sample tube orientation for quantitative desorption 51
13.2Tube conditioning 51
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QUI-0002 vs 5.2 September 2006
13.2.1Typical parameter settings for conditioning various sorbent tubes 51
13.2.1.1 Tenax TA / Tenax GR 51
13.2.1.2 Chromosorb 106 / Chromosorb 102 51
13.2.1.3 Carbopack B / Carbotrap / GCB1 / Carbopack C / Carbotrap C 51
13.2.1.4 Spherocarb / Unicarb / Carbosieve SIII / Carboxen 1000 / Carboxen 569 52
13.2.1.5 Molecular Sieve 13X, Molecular Sieve 5A 52
13.3 Cold Trap conditioning 52
14 'About' the UNITY user interface 53
14.1Windows platform 53
14.2Operating languages 53
14.3Status bar 53
15 UNITY Operation: System 'Ready' status 53
15.1Internal system checks 53
15.2Checks on external components of the analytical system 54
16 UNITY Options 54
16.1Method options 55
16.2Gas options 55
16.3Sequence options 55
16.4Port options 56
16.5Configuration options 56
16.6Report options 56
16.7Miscellaneous options 56
17 UNITY Methods 56
17.1Controlling method 56
17.2Generating a new method 56
17.3Saving a new method 56
17.4Opening a stored method 57
17.5General method file functions 57
17.5.1Copy method parameters 57
17.5.2Paste 57
17.5.3Print method 57
17.5.4Saving existing methods 57
18 Schematic display of UNITY status 58
19 Split on or off in standby 58
20 The Leak Test 58
20.1Description of leak test 59
20.2Main causes of Leak Test Failure 59
20.2.1Wearing of the O-rings which seal the tube 59
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20.2.2Interference with the tube seal by fibres and particles 59
20.2.3Damaged O-rings 60
20.2.4Leaking split filter tube seal 60
20.2.5Wearing of the cold trap seals 60
20.2.6Other causes of leak failures 60
21 Sample tube purge at ambient temperature 60
21.1Functions / objectives 60
21.2Control of the carrier gas flows during ambient purge 60
21.2.1Trap in or out of line 60
21.2.2Split on or off 60
21.2.3Determining the prepurge time 61
22 Desorption modes 61
22.1Tube conditioning mode 61
22.1.1Parameters 62
22.2Standard 2(3) stage desorption 62
22.2.1Parameters 62
22.3 Other operating modes 64
23 Sample tube purge at elevated temperature 64
24 Practical considerations for sample tube desorption 64
24.1 Sorbent maximum temperatures 64
24.2 Importance of desorption flow 65
24.3 Testing for complete desorption 65
24.4 Verifying desorption efficiency 66
25 Setting desorb and split flows 66
25.1 When should desorb / split flows be measured? 66
25.2The Set Gas Flow function 66
25.2.1What does the system do when I select Set Gas Flows 67
25.2.2Measuring and adjusting flows during Set Gas Flow 67
25.2.3To Exit the Set Gas Flows Function 68
25.3Gas flow constraints - Minimum settings, maximum settings 68
25.4Sample Splitting 68
25.4.1Calculating analyte masses in the sample tube 68
25.4.2Analytical column capacity 69
25.4.3GC system detection limits 69
25.4.4Calculating Splits 70
25.4.4.1 Zero split - splitless operation 70
25.4.4.2 Single split operation 70
25.4.4.3 Double split operation 71
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25.5Gas flow through the analytical column 71
25.6UNITY systems with the carrier gas supply to the GC analytical column controlled by 71
electronic pneumatic control (EPC)
25.7UNITY systems configured with the accessory for electronic mass flow control of the 71
split flow
26 The Trap Heat Function 72
26.1When should Trap Heat be used 72
26.2The Trap Heat Method 72
26.3What does the system do when I select Trap Heat 72
26.4Parameters for cold trap conditioning 72
26.5Selection of the trap low temperature in Trap Heat Method 72
26.6Selection of the Trap Hold time 72
27 Sample flow path - valve and transfer line - temperatures 73
27.1Construction materials 73
27.2Temperature ranges 73
27.3Transfer line to GC column connection 73
28 Minimum Carrier Gas Pressure Setting 73
29 GC Cycle Time 73
30 Start Run key 74
31 Stop sequence key 74
32 Method development 74
32.1Guidelines for parameter selection 74
32.1.1Tube Desorption 74
32.1.2Trap Desorption 75
32.2Method validation 75
33 Method linking 75
34 SecureTD™ - Re-collection for repeat analysis 77
35 Routine maintenance 77
35.1Packing tubes 77
35.1.1How to pack tubes 77
35.1.2Lifespan of tubes 78
35.2Conditioning tubes 78
35.3Long term storage of clean and sampled tubes 78
35.4Changing tube seals 78
35.5Changing tube filters 78
35.6Removing the cold trap 79
35.7Packing the cold trap 79
35.8Changing the cold trap seals 79
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35.9Changing the cold trap filters 79
35.10 Changing the charcoal filters 79
35.11 Replacing the fuse 80
36 Trouble shooting 80
36.1Contamination - The presence of artifacts in the chromatogram 80
36.1.1The carrier gas supply 80
36.1.2Contamination from the sample tubes or cold trap 80
36.1.3Other potential sources of contamination 81
36.2Poor Peak Shape / Peak Splitting 81
36.3Carryover of components of interest 81
36.3.1Carryover in the Sample Tube. 82
36.3.2Carryover in the cold trap. 82
36.3.3Carryover in other parts of the sample flow path. 82
36.4Poor precision 82
36.4.1Introduction of standards 82
36.4.2Low carrier gas pressures/flows 83
36.5Poor recovery/loss of sample 83
36.6Cold trap cannot attain its low temperature 83
36.7High Air/Water background when using MS detectors 84
36.8Persistent leak test failures 84
37 Diagnostics 84
38 Accessing product and support information on the world Wide Web 84
38.1Markes International Limited - Home Page and facilities 84
38.2Consumables and Spares 84
38.3Applications library 84
38.4Technical support 84
38.5Downloading software upgrades 85
38.6Automation accessories. 85
39 Trademarks 85
Appendix One - Uninstalling UNITY software from the computer 86
Appendix Two - Connecting UNITY to a GC / GCMS System 88
Appendix Three - Consumables catalogue and enquiry/order form 94
Appendix Four - UNITY Preinstallation Check List 96
Appendix Five - Electronic Pnuematic Control Module (UNITYe) 99
Appendix Six - Discontinued product 103
Appendix Seven - Multi-purpose Direct Inlet Accessory 104
Appendix Eight - Mass Flow Controller 114
7
1 Warnings and disclaimers
1.1 Electricity
Ensure that the mains cord is correctly wired and that the ground leads of all electrical units are connected
together via the circuit ground to earth.
Any work undertaken on the incoming AC line components should be performed by a qualified electrician.
UNITYTMmust be unplugged from the mains before any panels are removed.
1.2 Compressed gases
Handle cylinders of compressed gas with care. Avoid knocking valves and ensure that correct valves and
gauges are used. If possible, store and site gas cylinders outside the laboratory, firmly clamped in
position.
1.3 Hydrogen gas
Although hydrogen may be used as a carrier gas for standard GC and thermal desorption care must be
taken in case the high temperatures involved in thermal desorption cause hydrogenation of reactive
and/or unsaturated species.
2 UNITY Preinstallation Check List
2.1 Minimum computer specification for UNITY control
In general a PC with sufficient resources to run 32 bit Windows (95, 98, ME, 2000, XP, NT4(series 4)) will
have adequate performance for controlling UNITY. As such the minimum PC requirement recommended
is a 400MHz Pentium with 64MB RAM and a minimum of 20MB of free disc space (for the UNITY software
installation). A Windows compatible mouse is also required.
The user interface requires a minimum SVGA (800x600 pixel) screen resolution and ideally an XGA
(1024x768 pixel) screen resolution 256 colour in both cases.
The PC requires a free serial comms port for communication with UNITY. An additional serial comms port
is required for each of the following accessories: Air Server
TM
, U
LTR A
TM
, SecureTDTM, Headspace unit.
UniSense
TM
(UNITY plus sensor) requires two free serial comms ports.
UNITY communicates at 57600 baud. Whilst lower baud rates can be programmed, this is not
recommended as it will result in degradation of system performance (most modern PCs will support
communication at this speed).
A 9 way Null modem cable is supplied for connecting UNITY to the PC comms port.
The PC will also require an internet connection if the browser facility, included in UNITY's user interface,
is to be used. The browser is not required for system operation.
2.2 GC equipment requirements
UNITY is usually connected to a gas chromatograph configured with appropriate conventional or mass
spectrometer (MS) detectors. No conventional GC injector is required for UNITY operation. Ready and
external start connections are required on the GC.
2.3 Access into the GC oven
The UNITY heated transfer line is lined with 0.25 mm I.D., 0.35 mm O.D. uncoated deactivated fused
silica which butt connects with the capillary analytical column inside your GC oven. It is important that
the heated and insulated portion of the transfer line extends as far as the skin of the GC oven such that
the GC oven heating begins at the point where heating of the transfer line ends. A 25 mm diameter
access hole is thus required into the GC, with a 6.5 mm hole in the GC inner oven wall. Further
information is provided in Section 4.3.1.
2.4 GC configuration/parameter selection
From a GC perspective, UNITY may simply be regarded as a multipurpose, stand alone GC injector for
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QUI-0002 vs 5.2 September 2006
capillary or 1/8 -inch packed columns. No conventional GC injector is required for UNITY operation. The
rest of the GC system - column, oven, data handling, detector, etc. - should be configured and used, as
per normal chromatographic practice for the analytes of interest.
If multiple applications are to be carried out or if samples are uncharacterised; for example when
monitoring unknown atmospheres, a good general purpose GC configuration comprises 25-30 m,
0.25mm or 0.32 mm ID, 1 or 2 µm phase thickness bonded methyl silicone capillary column with
a FID or mass spectrometer detector.
2.5 Laboratory location
2.5.1 Space requirements
UNITY occupies minimal bench space, being only 12 cm wide, and can sit either side of the gas
chromatograph.
2.5.2 Recommendations relating to the quality of the laboratory air
UNITY is a powerful concentration device and is often used to determine trace levels of organic analytes.
It is advisable to store and operate UNITY in a clean
laboratory environment with minimal atmospheric
concentrations of organic vapours.
2.5.3 Recommendations relating to the quality of the laboratory gas lines
As UNITY is a concentrator, even trace level contaminant’s in laboratory gas lines can become
significant interferents in the chromatograms produced. It is recommended that gas lines be constructed
of refrigeration-grade copper tubing connected using approved swage-fittings. Laboratory gas line joints
and connections must never be brazed. Position the gas supplies as close as possible to the analytical
system i.e. such that the gas lines are as short as possible. Use a high quality, stainless steel diaphragm
cylinder head regulator for the carrier gas supply.
2.6 Services
2.6.1 Power
UNITY is automatically compatible with all conventional mains power supplies ranging from 90 to 255 V
and 50 or 60 Hz. It is not necessary to manually select or switch voltages. The maximum power
consumption of UNITY is 400 W.
2.6.2 Pressure controlled supply of dry air or nitrogen
2.6.2.1 Functions
UNITY requires a pressure-regulated supply of dry air or nitrogen at between 55 and 70 psi both to
actuate the main valve and to purge the cold trap box.
Note:
The dry air / nitrogen supply is critical and UNITY must never be switched or left on
without this gas supply.
For UNITY prior to serial number U-10235 the dry air/Nitrogen the UNITY should never be switched on
without the supply of dry air / Nitrogen.
UNITYs with serial number greater then U-10235 has a built in sensor to prevent damage to the Peltier
cell, in the event that UNITY is run without the dry air / Nitrogen supply being switched on. The UNITY
status bar will read "Equilibrating" and the Trap temperature will not reach the temperature set.
It is recommended that a secondary pressure regulator be used to control the supply of dry gas to
UNITY in addition to that controlling the general laboratory line pressure. Any conventional pressure
regulator should suffice for this and suitable pneumatic control may already be available on your GC.
Alternatively, Markes International Ltd. supply a pneumatic control accessory (P/N U-GAS01) for both
air and carrier gas - see section 2.6.3.3. It is recommended that the pressure in the laboratory air line
be 10 psi higher than that supplied to UNITY.
2.6.2.2 Specification required (dryness / purity)
The compressed air or nitrogen must be dry (dewpoint lower than -35°C.) Conventional air
compressors / nitrogen generators may be used provided the gas produced is adequately dried.
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QUI-0002 vs 5.2 September 2006
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QUI-0002 vs 5.2 September 2006
2.6.2.3 Consumption
Dry air or nitrogen flows at <200 ml/min into the cold trap box creating a slight positive pressure and
minimising ingress of water from the laboratory atmosphere. If the cold trap box was not purged, ice
would quickly build up around the Peltier cell which is maintained at -25°C throughout UNITY operation.
Gas consumption for valve actuation is minimal.
2.6.3 Pressure controlled carrier gas supply
2.6.3.1 Gas selection - type / purity
Helium is invariably used as the carrier gas for capillary chromatography and nitrogen for packed
column or sensor work. 5.0 grade (i.e. 99.999%) or higher purity gas is recommended in either case.
Although Hydrogen may be used as a carrier gas for standard GC and thermal desorption applications,
care must be taken in case the high temperatures involved in thermal desorption cause hydrogenation
of reactive and / or unsaturated species.
2.6.3.2 Line pressures and recommended pneumatic control
UNITY requires a regulated supply of carrier gas at a pressure to suit the analytical column / system
selected. The UNITY gas flow path has minimum (<2 psi) impact on total system impedance. Suitable
pneumatic control for the carrier gas may already be available on your GC. The performance of most
common capillary columns is optimised at between 1 and 2 ml/min typically requiring between 10 and
30 psi head pressure. High quality pressure regulators incorporating a stainless steel diaphragm are
recommended for carrier gas control. The pressure in the laboratory carrier gas line should be at least
10 psi higher than that supplied to UNITY.
2.6.3.3 UNITY and Electronic Pneumatic Control (EPC)
(Only relevant for installations on Agilent 6890GCs - see Appendix Five)
For optimum performance the carrier gas pressure to the EPC module should be regulated to
approximately 15 to 20 psi above the column head pressure.
Note:
As EPC only controls the carrier gas, suitable pneumatic control of the dry gas will still be
required. A U-GAS01 from Markes International includes a carrier gas regulator to step down the
carrier pressure and a separate regulator and gauge for control of the dry air or nitrogen, and is
therefore recommended in this case.
Note:
When installing onto an existing 6890GC the firmware on the GC must be A.03.08 or later (for Aseries) or N.04.09 (for N-series). To check the firmware version, use the keyboard on the GC press:
Options > Diagnostics > Instrument Status and then scroll down to 'Version' where you will see the
version of the firmware running on the instrument.
2.6.3.4 Filters
Deoxo and organic filters should be included in the carrier gas line just upstream of connection to the
UNITY-GC analytical system.
3 System description and summary of operation
(For more detailed information, see Section 22.)
3.1 Parameters and ranges
See Table 1 below
3.2 Sample flow path and key system components
A detailed schematic of the UNITY flow path in Standby Mode is shown in Figure 2. Key components
include the heated valve (material: PTFE), cold trap (material: quartz), transfer line (material: uncoated,
deactivated fused silica) and connecting tubing (Silcosteel.)
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QUI-0002 vs 5.2 September 2006
Parameter Range
Mode Standard 2(3) Stage Thermal Desorption
Tube Conditioning
Direct Sampling (only applicable if UNITY is used
in conjunction with multi-purpose Direct Inlet
Accessory)
On Line Air (only available if UNITY is used in
conjunction with Air Server)
Split on in standby Yes/No
Ambient temperature carrier gas purge Time settable between 0.0 and 99.9 minutes in 0.1
minute increments.
Split on during tube purge Yes/No
Trap in-line during tube purge Yes/No
Elevated temperature purge or stage 1 of primary
(tube) desorption (optional)
35.0 to 350.0°C (settable in 1° increments) for 0 to
999.9 minutes (settable in 0.1 minute increments)
Trap in-line during elevated tube purge Yes/No
Split on during elevated tube purge Yes/No
Primary tube desorption (stage 2 if optional
elevated temp. purge employed)
50 to 380°C (settable in 1° increments) for 0 to 999
minutes (settable in 0.1 minute increments.)
Split on during primary (tube) desorption Yes/No
Cold trap focusing temperature -15 to +50°C (settable in 1° increments.)
Cold trap (secondary) desorption temperature
minutes.
50 to 400°C (settable in 1° increments) for 0 to 99.9
(settable in 1 minute increments.)
Cold trap heating rate Max (ballistic heating reaching 100°C/sec during
first critical stages of trap heat) or options between
1° and 40°C/sec
Split on during secondary (trap) desorption Yes/No
Flow Path Temperature 50 to 210°C
GC Cycle Time 0 to 999.9 minute
Minimum Carrier Gas Pressure 0.0 to 99.0 psi
N.B. At least one of these
options must be selected
N.B. At least one of these
options must be selected
Table 1. Parameters and Ranges for UNITY thermal desorber
3.3 Operational sequence for 2(3) stage desorption mode
(For more detailed information, see Section 22.)
When a tube is placed and sealed into the flow path of UNITY for conventional 2(3) stage desorption, it
undergoes the following sequence of operations:
Standby (Figures 1 and 2)
Options: - Split flow on or off
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QUI-0002 vs 5.2 September 2006
Figure 2. Detailed Schematic of UNITY flowpath in Standby Mode (split off)
Figure 1. Simplified schematic of the UNITY flowpath in standby mode
Sample tube Cold trap Analytical column
Optional split flow
Carrier Inlet
Pressurise (Figure 3)
Note:
The pressurise stage is actually an inherent part of the leak test and therefore does not appear
as a stage on the UNITY status bar (Section 14.3).
Leak test (Figures 4a and 4b)
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QUI-0002 vs 5.2 September 2006
Analytica
Sample tube
Cold trap Analytical column
Carrier Inlet
Figure 4a. Simplified schematic of the UNITY flowpath in leak test mode of sample tube and cold trap
Sample tube
Cold trap Analytical column
Carrier Inlet
Figure 3. Simplified schematic of UNITY flowpath in pressurising sample tube and cold trap mode
Figure 4b. Detailed schematic of UNITY flowpath in leak test mode
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QUI-0002 vs 5.2 September 2006
Ambient temperature purge (Figures 5a, 5b and 6)
Options: - Split flow on or off
Cold trap: - in or out of line
Note:
Either the split flow or the desorb (trap) flow or both must be open during the purge.
Carrier Inlet
Figure 5a. Simplified schematic of the UNITY flowpath in ambient temperature purge mode -
cold trap off line
Split flow
Analytical columnSample tube Cold trap
Figure 5b. Detailed schematic of UNITY flowpath in ambient temperature purge mode -
cold trap off /on line
Elevated temperature purge (optional) (Figures 7a and 7b)
Options: - Split flow on or off
Cold trap: - in or out of line
Note:
Either the split flow or the desorb (trap) flow or both must be open during the purge
Primary (tube) desorption (Figures 8a and 8b)
At the start of primary (tube) desorption the tube oven begins to heat (either from ambient or from the
temperature of the optional elevated temperature purge if selected). Note that the tube desorption
time is measured from the beginning of tube oven heating and not from the time at which the
sample tube reaches its desorption temperature.
Options: - Split flow on or off
15
QUI-0002 vs 5.2 September 2006
Analytical columnCold trap
Sample tube
Carrier Inlet
Split flow
Figure 7a. Simplified schematic of UNITY flowpath in elevated temperature purge mode - cold trap off line
Figure 7b. Simplified schematic of UNITY flowpath in elevated temperature purge mode - cold trap on line
Sample tube
Analytical column
Optional split flow
Cold trap
Carrier Inlet
Desorb flow
Figure 6. Simplified schematic of UNITY flowpath in ambient temperature purge mode -
cold trap on line
Sample tube Cold trap
Carrier Inlet
Optional split flow
Desorb flow
Analytical column
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Figure 8b. Detailed schematic of UNITY flowpath in primary (tube) desorption mode
Figure 8a. Tube Desorption - Series of simplified schematics showing analytes being desorbed from the
sample tube to the cold trap
Pre-Trap Fire Purge (Figure 9)
Following primary desorption, the heated valve is moved and carrier gas is flushed through the split tube
and the trap to remove any residual air and water prior to trap injection. It may also be used to dry purge
the cold trap prior to injection when direct desorbing solid or humid samples.
This purge step is pre-set to run for 18 seconds. If the user requires a different purge time this can be
set in View > Options > Sequence section of the UNITY software (Section 16.4)
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QUI-0002 vs 5.2 September 2006
Figure 9. Detailed schematic of UNITY flowpath in pre-trap fire purge mode
Secondary (trap) desorption (Figure 10a & b)
Options: - Split flow on or off
Note that the flow path of UNITY remains in the trap desorption configuration until the trap has
cooled back down below 50°C.
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QUI-0002 vs 5.2 September 2006
Figure 10b. Detailed schematic of UNITY flowpath in Secondary (trap) desorption mode.
Figure 10a. Trap Desorption - Series of simplified schematics showing analytes being desorbed from the
cold trap to the analytical column and the sorbent tube cooling to ambient
3.4 Operational sequence for tube conditioning mode
(See Section 22.1 for further details)
The first four stages of operation in tube conditioning mode; - standby, pressurise, leak test and ambient
purge are identical to those described above for 2(3) stage desorption (Figures 2 to 6.)
Stage five of tube conditioning is primary (tube) desorption with the split flow on and the cold trap off-line
(Figure 7.)
3.5 Sample tubes
UNITY is compatible with industry standard sample tubes - 3.5-inches (89 mm) long by 1/4-inch (6.4 mm)
O.D with 5 mm (stainless steel and coated steel) or 4 mm (glass) I.D.. Sorbent is retained in stainless
steel (or coated steel) tubes using stainless steel (or coated steel) gauzes and a gauze retaining spring.
Quartz or glass wool is recommended for retaining the sorbent in glass tubes.
3.6 Tube desorption oven
The UNITY tube desorption oven heats up rapidly (~150°C/min) at the start of elevated temperature purge
or tube desorption. It begins to cool at the end of primary (tube) desorption and reaches 50°C from 300°C
within 10 minutes.
3.7 Tube filters and seals
When ready for analysis, sample tubes are placed into the cool desorption oven with the sampling
(grooved) end pointing to the rear of the instrument. Operation of the lever mechanism seals the sample
tube into the UNITY flow path. Temperature resistant Viton O-rings seal onto the outer wall of the sample
tube, ~2 mm from either end. Each O-ring should last for >1000 tube-sealing operations. In the event of
failure, O-rings at both ends of the sample tube are readily replaced by the user. (See Section 35.4.)
A porous PTFE filter sits just behind the O-ring in both sample tube seals. These prevent UNITY flow
path contamination in the event that sorbent particles or high boiling sample materials migrate out of the
tube. The filters are readily accessed for user replacement. (See Section 35.5.)
3.8 The cold trap
The cold trap contains a 2 mm diameter x 60 mm long bed of sorbent (30 to 100 mg depending on sorbent
density) supported by quartz or glass wool. Note that the length of the first plug of glass wool is
included in the total 60 mm sorbent bed.
3.9 Cold trap cooling and heating
UNITY contains a 2-stage peltier cell, which uniformly cools the entire 60-mm sorbent bed to a minimum
of -10°C in ambient temperatures as high as +30°C. N.B. The minimum is reset at -15°C for ozone
precursor systems. At -10°C, a cold trap packed with an appropriate series of sorbents including
carbonised molecular sieve, allows quantitative retention of compounds as volatile as ethene and freons
from over 500 ml of gas/air. No liquid cryogen is required. With the trap at -15°C quantitative recovery
of ethyne can be demonstrated from over 200 ml of gas/air.
Note:
C2hydrocarbons (ethyne, ethene, ethane) and the most volatile freons cannot be sampled using
sorbent tubes at ambient temperatures - Breakthrough volumes are too small for practical use even with
the strongest tube sorbents. These compounds must be collected in bags or canisters or sampled on
line. These whole air/gas samples are then introduced to the UNITY cold trap using an Air Server
Accessory.
Once all the target analytes have been collected and focused in the cold trap, the trap oven heats
ballistically reaching rates in excess of 60°C/sec for the first critical stages of trap desorption.
Uncompromised capillary chromatography is produced without on-column focusing and with desorption
flows as low as 2 ml/min. This facilitates splitless operation with high-resolution capillary GC.
3.10 Gas flow through the cold trap
The UNITY cold trap operates in backflush mode - the sample gas stream enters and leaves the cold trap
through the narrow-bore/restricted end which points to the rear of the instrument. Backflush desorption
allows use of a series of 2 or 3 sorbents of increasing strength in the cold trap - For example; Tenax TA
TM
19
QUI-0002 vs 5.2 September 2006
(weak) backed up by Carbograph 1TD TM(medium), backed up by UniCarb
TM
(strong). This facilitates
the analysis of wide volatility range samples. (High boiling compounds are retained by and quantitatively
desorbed from the first weak sorbent, without ever coming into contact with the stronger sorbents behind.)
3.11 Trap filters and seals
As with the sample tube, the cold trap is sealed into the gas flow path of UNITY via O-rings, which seal
on the outer wall of the trap tube. At the cool non-valve end of the trap, the O-ring is backed up with a
porous PTFE filter to prevent contamination of the pneumatics in the event of sorbent particles migrating
out of the trap. The user has access to this O-ring seal and filter in the brass trap connector (Section 4.2),
but a Service visit is required to access and change the trap O-ring seal in the heated valve.
As the cold trap is only changed infrequently, the seals will rarely, if ever, need to be replaced. It is
recommended that UNITY is professionally serviced once per year and that the valve-end seal be
changed as part of this annual maintenance operation.
3.12 Split filters
There is a split filter tube packed with charcoal (P/N UTD-5065) on the split line upstream of the on/off
solenoid and needle valves. This prevents contamination from the sample reaching the valves or
laboratory air. The flow path up to the charcoal filter is heated and constructed of inert, Silcosteel®tubing.
The filter itself is the same size as a standard sample tube and may be readily replaced by a clean sorbent
tube if the split effluent is to be re-collected for repeat analysis, see Section 34. The split filter (or recollection tube) is sealed into the split flow line using easy-connect, Viton O-ring seals and by operating
a lever in the same manner as the sample tube. The sampling end/grooved end of the re-collection tube
should point to the rear of the instrument.
Conventional charcoal split filters will become contaminated over time and should be reconditioned or
repacked when required (Section 35.10.)
3.13 User interface
UNITY is controlled from an IBM or compatible PC via software operating in a 32 bit Windows™
environment (Windows 98, ME, 2000 or NT4). Everyone familiar with Microsoft®Office and related
Windows products should readily understand the interface.
4 UNITY Installation
4.1 Packing list
The following items are contained in your UNITY shipment. Please inform your distributor immediately if
there are any shortages. Items marked with a * are consumable items and may require replacing at
intervals. These items are available in various pack sizes and the commercial part numbers required to
re-order them are given in the ‘Focusing on Volatiles’ brochure included at the back of this manual.
Alternatively further information may be found on our web site www
.markes.com
20
QUI-0002 vs 5.2 September 2006
Part No. Description Qty
General Parts
U-UNITY(e) UNITY(e) instrument 1
UTD-5003 Transfer line 1
UTD-1165 Perspex cover 1
U-SW001 Software CD 1
U-T2GPH* General Purpose Cold Trap (packed with sorbent) + Trap Certificate 1
Z-0024 Mains cable (suitable for your geographic location) 1
21
QUI-0002 vs 5.2 September 2006
Part No. Description Qty
Documentation
UTD-9001 User Manual and Brochure Pack 1
QUI-1014 UNITY Quick Reference Guide 1
UNITY common parts - shipping kit
UTD-5105* Sampling tube packed with Tenax TA. Conditioned and capped with ¼-
inch brass SwageLok type caps fitted with combined PTFE ferrules.
Etched with a unique serial number
1
UTD-1050* Disc Sintered PTFE 5.1mm 2
UTD-1074* Disc Sintered PTFE 6.5mm 2
UTD-1125 Autosystem Clamp 1
UTD-5062 Tube Extractor 1
UTD-5063 Tool Kit (standard) 1
UTD-5064 Trap Alignment Tool 1
UTD-5065 Split Filter Tube Packed with Charcoal (unetched) 1
UTD-5093* Fused Silica Transfer Line Insert 1.5m & PTFE Sleeve 1
Z-0026 Union 1/8 "x 1/8" Brass SwageLok 1
Z-0050 Union Reducer 4 mm x 1/8" Brass 1
Z-0055 Tubing Plastic 4mm 1m
Z-0087* O-ring Size 006 Viton 2
Z-0089* O-ring Size 010 Viton 4
Z-0092* O-ring 3mm ID, 1mm Section 2
Z-0097* Quick Seal Connector and Instructions 2
Z-0145 Tube Copper 1/8” - 3M 1
Z-0157 Nut 1/16 St St Swagelok 1
Z-0189 Cable PC 1
Z-0283* Ferrule 1/16 Graph. Vesp. 0.4mm 2
Z-0285 O-ring Insertion Tool 1
Z-0351 O-Ring Extraction Tool 1
Z-0372 Washer 1/4” x 1 1/2” 2
Z-0371 Washer 1/4” x 1” 2
Z-0449 Washer 1/4” x 2” 1
Z-FS6A3 Fuse 5mm x 20mm 6.3anp Antisurge 1
Z-NM4FSS Nut M4 St St 4
For UNITY
UTD-5095 PCB GC Interface for UNITY + GC 1
4.2 Installing the cold trap
4.2.1 Trap sorbent selection
As a general rule, because it is maintained at sub ambient temperatures, sorbent selection is less critical
for the trap than the sample tube.
For most applications involving VOCs ranging from C
5
- C32, a trap containing ~ 30mm bed of Tenax TA
backed up by ~ 30mm Carbograph 1TD
TM
separated and supported at each end by unsilanised glass
wool plugs, will suffice. (P/N U-T2GPH)
Traps containing the three sorbents Tenax TA backed by Carbograph 1TD
TM
backed by Carboxen
1000
TM
each separated and supported by unsilanised glass wool plugs would be ideal for focusing
compounds ranging from C2- C24. (P/N U-T4WMT).
Note:
This type of trap will retain a small % of water and therefore requires very careful selection of
analytical conditioning parameters. (See Section 13.3)
4.2.2 Packing the cold trap
Note that ready-packed traps are available from Markes International Ltd. Please see Table 3 for details.
Empty trap tubes (P/N U-T7EMP) are also available for the user to pack as required. The UNITY cold
trap is constructed of quartz and has an O.D.of 2.9 mm, and an I.D. of 1 mm at the inlet / outlet end and
an I.D. of 2 mm at the other end. It is fragile and should be packed with care.
Empty cold traps should be packed from the wider (2 mm) bore end using the following procedure. First
insert a 2-5 mm plug of quartz or glass wool using a suitable flexible tool such as a 15 cm length of 1/16
-inch, narrow bore plastic tubing (PTFE or PEEK tubing is ideal.) Pour in the required amount of sorbent.
Note:
A 6 cm length of the wider bore section of the trap tube, measured from the point of the bore
restriction, is subjected to full cooling and heating power.
The trap packing, including all but the back glass / quartz wool plug, should be within this 6 cm length
22
QUI-0002 vs 5.2 September 2006
Part No. Description Qty
For EPC ready UNITYe
UTD-5098 PCB GC Interface for UNITYe 1
EPC parts for installation on 6890/6850GC
Z-0026 Union Brass 1/8” - 1/8” 2
Z-0040 Ferrule 1/8” x 1/16” Graph Vesp 5
Z-0108 Tube PEEK 1/16” OD x 0.03” bore 3m
Z-0402 Ferrule 1/8” x 2mm Graph Vesp 1
Table 2. Packing List for UNITY thermal desorber
Glass wool plug
Glass wool plug
6 cm - from start of glass wool plug at front, restricted
end of trap - to the end of the packing
Figure 11. A packed UNITY cold trap
Inlet / outlet end
restricted to < 1 mm
bore to enhance linear
velocity
Packing Retaining
spring
of the trap (Figure 11.) Note that analytes enter and desorb from the trap through the restricted end.
Multibed traps must therefore be packed with the sorbents arranged in order of increasing strength from
the narrow end. (See notes on sorbents in Section 8.1.) 1 to 3 mm plugs of quartz wool must separate
different sorbents. Plug the end of the trap with another glass wool plug, backed with a packing retaining
spring. If unsilanised glass (rather than quartz) wool is used in the cold trap, it may cause degradation
and / or tailing of polar and labile compounds. Silanised glass wool does not suffer from these limitations
but must not be taken above 275 °C or breakdown products from the silylating reagent will coat the
sample flow path of the desorber, reducing recovery of high boiling compounds.
Note:
Do not over-compress the cold trap packing as this will cause high impedance, which may limit
trap desorption flows. If high trap desorption flows will be required, for example when using a high split
ratio, use 40-60 rather than 60-80 mesh sorbent.
4.2.3 Cold trap installation
Once UNITY and its accessories have been taken out of the main packing box, lift off the black perspex
cover. N.B. The perspex cover is supplied with a modification for optional addition of automated
sampling. Tilt the front upper panel of the instrument forwards and away from the rest of the instrument
on its hinge (Figure 12.) Find the Pozidriv™ screwdriver supplied as part of the standard tool kit within
the shipping kit.
Hook the screwdriver under the far side of the hinge as shown in Figure 12 and push firmly upwards and
towards the back of the instrument. This separates the hinged cover from the rest of the instrument. Put
the cover to one side.
Note:
The carrier gas supply to the instrument and the instrument itself must be turned off before using
23
QUI-0002 vs 5.2 September 2006
Part Number Name Application
U-T1HBL High Boilers Trap Suitable for VOCs from n-C6to n-C
40
U-T2GPH General Purpose Hydrophobic
Trap
Suitable for VOCs from n-C
4/5
to n-C
30/32
U-T3ATX Air Toxics / TO-14 Trap Suitable for VOCs from n-C2to n-C
12
U-T4WMT Water Management Trap Suitable for VOCs from ethane to n-C20-
allows selective elimination of some water but
is less hydrophobic than the ‘General Purpose
Hydrophobic’ trap
U-T503F Ozone Precursor / Freons Trap Suitable for Ozone Precursors from acetylene
to trimethyl benzene and Freons
U-T6SUL Sulphur Trap Suitable for volatile, reactive species such as
sulphur containing compounds
U-T7EMP Empty Cold Trap
U-T8CUS Custom packed Cold Trap
U-T9TNX Tenax Cold Trap For selective elimination of volatiles and for
other general TD applications with target
analytes ranging in volatility from n-C
6
to n-C
32
U-T10CW Chemical Agents Trap For high boiling compounds such as Chemical
Warfare agents and phosphorus pesticides
U-T11GPC General Purpose Graphitised
Carbon Trap
Recommended for EPC operation, suitable for
VOCs from n-C
4/5
to n-C
30/32
(NB not suitable
for thermally labile compounds)
Table 3. List of UNITY Cold Traps available from Markes International
the following procedure to install or replace a packed cold trap.
Using the 7/16 x 1/2" AF wrenches
(spanners) provided in the tool kit,
undo the 1/8-inch brass nut
connecting the 1/16 -inch peek
tubing to the front of the desorb
pneumatics panel. (Figure 12) Undo
the nut (labeled as nut B in figure 13)
furthest from the solenoid valve on
the 1/16 x 1/16-inch union
connecting the desorb pneumatics
assembly to the carrier bypass line
(Figure 13). Pull the wire harness
out of its retaining clip and uncouple
the black plug in the middle of the
harness.
Using the Pozidriv screwdriver supplied in the tool kit, loosen the screw at the bottom of the desorb
pneumatics assembly - marked A in Figure 13 - Loosen screw A by ~4 turns. Do not remove the screw
completely. Gently pull the desorb pneumatic assembly towards the front of the instrument being careful
to keep it in the horizontal plane by keeping screw A inside the slot in the pneumatic assembly base
plate. The swivelling brass trap connector will usually be left attached to the pneumatics as they are
withdrawn (Figure 14.) Once clear of screw A, pull the pneumatics forward and rotate to the left thus
providing sufficient space to insert the cold trap.
The sample enters and leaves the cold trap from the narrow bore end via the heated valve. The cold
trap should be positioned in the cold trap box such that the narrow bore end is nearest the heated valve
- i.e. pointing to the rear of the instrument.
24
QUI-0002 vs 5.2 September 2006
Figure 12. Removal of the front hinged panel
Wire harness
removed from
its clip and
disconnected
A
Nut B
Figure 13. Loosening the pneumatic assembly for cold trap insertion
Remove the packed cold trap from its packaging along with the two small Viton spacer O-rings (Z-0092)
from the shipping kit. Place the two O-rings within 20 mm of the wide bore end of the trap (Figure 15.)
Gently push the restricted / narrow-bore end of the trap tube into the cold trap box. You will feel
increased resistance as the cold trap pushes into the seal at the valve end. DO NOT APPLY
EXCESSIVE FORCE TO THE QUARTZ COLD TRAP TUBE - swizzling (turning) the cold trap slowly
with your fingers as it is pushed into the cold trap box can make installation easier. Before installing a
cold trap tube for the first time or whenever in doubt about how much force to apply or the locations of
the various system components practice once or twice using the trap alignment tool supplied with the
shipping kit.
Note:
NEVER SWITCH UNITY ON WITH THE TRAP ALIGNMENT TOOL INSTALLED.
The trap seals are already aligned and gentle, steady pressure should be sufficient to push the tube into
the valve seal. Approximately 11 mm of quartz tube should be protruding beyond the face of the white
PTFE sealing disk once the trap tube is properly located. Bring the pneumatic assembly back and
relocate screw A in the slot on the pneumatic assembly base plate. Take care here that the brass trap
25
QUI-0002 vs 5.2 September 2006
Figure 14. Pneumatics assembly withdrawn
Screw A
Brass trap connector
Figure 15. Inserting the quartz cold trap tube
2 Viton
spacer
O-rings
PTFE trap
sealing disk
Front plate
of split
pneumatics
Front plate
of main
pneumatics
connector does not hit the end of the quartz cold trap. Push the assembly gently back in the horizontal
plane guided by screw A. Apply gentle steady pressure to push the trap into the sealing O-ring located
inside the brass trap connector.
Note:
When the trap tube and connector are correctly positioned, the front plate of the main pneumatic
assembly should align closely with that of the split pneumatic assembly. Retighten screw A firmly and
reconnect the unions and gas connections. Reconnect the plug in the electrical harness and replace it
in the clip on the pneumatics front plate.
4.3 Installing the transfer line
UNITY is supplied with a universal transfer line to convey desorbed analytes from UNITY to a gas
chromatograph or other analytical system. The sample path utilises a deactivated fused silica line
(0.25mm I.D. and 0.35mm O.D.) heated over its entire length by means of a distributed heater and at the
GC end by heat conduction from the GC oven.
The line is 1m long, which is sufficient to reach most gas chromatographs even when a mass
spectrometer is attached.
4.3.1 Connecting the transfer line to the gas chromatograph
Most GCs have built in access to the oven region by means of holes in the side, top or back of the oven,
with "knock out" sections in the outer casing.
If all such access points are already in use it is possible to gain entry via an unused injector or detector
port with or without a heated zone.
The general approach is illustrated in the three diagrams, figures 16, 17 and 18, and the simplest entry
s shown in Figure 16.
Note:
In all cases, the fused silica line and PTFE sleeve tubing are fitted as the final operation.
Locate a hole in the inner oven wall with a corresponding hole leading to the outside of the instrument.
It is usually necessary to displace the oven insulation material to enable the flexible metal line to be
pushed against the outside of the inner oven wall.
If the GC oven wall insulation is particularly thick it may be necessary to shorten the silicone foam rubber
insulation sleeve, which is intended to rest against the outer wall of the GC oven.
The M6 spacer nut (attached to a 1/4-inch spacer tube on the transfer line) secures the line casing to
the oven wall allowing the 1/8-inch aluminium sleeve to protrude into the oven. If the hole in the inner
oven wall is larger than the end of the line, fit one of the large metal washers from the shipping kit at this
point.
26
QUI-0002 vs 5.2 September 2006
End of line heater
Spacer nut (M6)
Aluminium heat
conductor
PTFE protective sleeve tubing
0.25 mm I.D. fused silica
Inner wall of GC oven
GC oven insulation
Outer wall of GC
oven
Silicone foam
rubber insulation
Figure 16. Connecting the transfer line through the outer casing of the gas chromatograph
27
QUI-0002 vs 5.2 September 2006
In figure 17 the entry to the GC oven is through the fan protection grill. In this situation the 1/4-inch
spacer tube attached to the transfer line prior to the spacer nut is used to extend the line and a special
U-shaped metal support bracket is pushed through adjacent holes in the grill to press against the oven
inner wall.
Note:
The line must not be secured with a nut against the fan grill as this could be distorted causing it
to hit the fan.
Engineers with detailed knowledge of the GC may wish to remove the fan grill and secure the line as in
Figure 18 which shows installation via a heated zone block. As the entry hole will generally be larger
than the diameter of the metal line sleeve, one or more of the large washers supplied will be needed. If
the heated zone block is particularly deep both the M6 spacer nut and spacer tube will be needed as
shown.
This part of the line derives its heat from the heated zone block which should be set to run at a
conveniently high temperature, preferably 50°C above the line setting but not above 250°C as the
silicone foam rubber insulation will be damaged.
The parts supplied can be used in other combinations to suit particular instrument configurations.
U shaped metal
support bracket
Spacer nut (M6)
Spacer tube
Fan protection grill
Aluminium heat
conductor
Silicone foam
rubber insulation
Figure 17. Entry through the fan protection grill
Figure 18. Installation via a heated zone
Spacer nut (M6)
Spacer tube
Spacer nut (M6)
Heated zone block
Large washer
Large washer
Silicone foam
rubber insulation
4.3.2 Installing the fused silica transfer line insert
Once the heated line has been fitted to the GC, the fused silica plus associated PTFE sleeving (see
shipping kit) are pushed from the GC end, along the 1/8-inch aluminium tube until they protrude from the
other (UNITY) end of the transfer line.
4.3.3 Connecting the transfer line to UNITY
Place UNITY on the bench on the most convenient side of your gas chromatograph. Ensure that the
transfer line will reach from the top of UNITY to the selected entry point into the GC oven.
Ensure that UNITY is switched off and cool. Remove the rear top cover on UNITY by unscrewing and
removing the black knob on the rear outer cover (Figure 19). The rear cover is then free to slide
backwards and away from the instrument. If the air inlet pipe is in place this must be removed.
(This is a push fit coupling, to release the tube press on the outer ring and at the same time pull the tube).
The top of the heated valve is now exposed, as shown in figure 20.
Figure 21 shows a partly sectioned view of the completed assembly while figure 22 gives detail of the
position of the end of the fused silica tube inside the drilled out end of the Silcosteeled tube from the
heated valve.
28
QUI-0002 vs 5.2 September 2006
Figure 19. Photograph showing black knob
fixing rear top cover to UNITY
Black knob
Figure 20. Photograph of the heated valve
Figure 21. Partly sectioned view of the
transfer line connection to UNITY
Silicone foam
rubber insulation
Clamp plate
PTFE plate
Support plate
Shield tube
End of
heater
Tube coupling
Slot
Rear cover
Figure 22. Tube coupling detail
Fused silica
1/16-inch Silcosteel
tubing (0.5 mm
bore)
Analytes
from the trap
via the
heated valve
Bore of tubing
drilled out
Carrier bypass
Fused silica
terminates
here
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