Thermo Scientific EA IsoLink IRMS System Operating Manual page 68

2
Analytical Principles
Pneumatic Circuit
The valves are controlled by Isodat Software Suite. The split ratios are set by needle valves which are
located above the isothermal GC oven. The needle valves are preset.
Note Any changes may have influence on the system performance and should be done only when
necessary and after reading this manual.
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He Working Principle
When working with He
1. Analysis mode
2. He save mode
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He is switched on as default. It can be switched off if no He savings are desired.
• Combustion — Before an analysis Isodat uploads an EA method to the EA. This method includes
the settings of carrier and reference flow (=purge flow). It is thus obligatory that an EA method is
set in the sequence of Isodat to ensure proper functionality of the He
of the EA method the flows are set.
During initialization of the system (magnet settings, peak center, reference gas flow equilibration
in the ConFlo) the reactor flow (carrier gas) is stabilized.
When the sample drops (or is injected by liquids autosampler) the carrier gas flow is maintained
for a fixed period until all analyte gases produced upon conversion of the sample in the reactor are
certainly on the chromatographic column (analysis mode). Split valve 2 (EV2) is open at that time.
In general, the flow through the chromatographic column is 50 mL/min if the carrier flow is set to
180 ml/min. The split flow is thus 130 mL/min and merges into the reference gas (purge) line to
contribute to a sufficient purge flow of the sample in the autosampler (100 – 200 mL/min).
The minimum flow for the reference should be 10 mL/min.
As soon as all analyte gases are on the chromatographic column EV2 is closed and the carrier gas
flow is automatically set to 50 mL/min (He save mode). The reference flow is kept at its set value
(10 - 70 mL/min) but the contribution from the split is stopped. This status is maintained until
the next analysis is started.
40 EA IsoLink IRMS System for CNSOH Operating Manual
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module the analysis is separated into two phases:
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module. With the upload
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