GC cycle time

hi,

Im currently running a headspace method where Im getting very poor reproducibility in peak area.

I want to make sure that my GC cycle time is set to its correct value and that my vials are not spending enough or too much time on the carousel. the current cycle time is set to 46min based on the below parameters.

1. vial equilibration is 60min

2. vial pressurization is 0.4min

3. loop equilibration is 0.2min

4. inject time is 0.5min.

5. run time is 32min, the GC must cool down from 245C to 35C which takes probably 5-6min.

therefore would my cycle time be around 95min?

the GC is 7890A

thank you

0 Lance Nelson 2 months ago

The GC cycle time should be the time from injection until the GC is ready to run again. This includes the analysis run, cool down, and equilibration. Based on the times you listed, it would be roughly 40 minutes. It may be worth timing to make sure. The headspace sampler itself will add the vials to the oven for equilibration based on the cycle time. If the headspace oven has room for multiple vials (G1888, 7697 111-vial version, 8697) the second vial will be moved into the oven while the first one is still equilibrating. If the headspace oven can only heat one vial at a time (7697 12-vial version), then the vial equilibration is the limiting factor.

See also this post from another person asking about the same thing: Optimizing the total run time of a run using a GC 7697A Headspace system - Forum - Gas Chromatography - Agilent Community
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