Shift ret.time ONLY SECOND HALF CHROMATOGRAM

Discussions about GC and other "gas phase" separation techniques.

19 posts Page 2 of 2
MichaelVW wrote:
CrisTheChemist wrote:
peak at 12.0min is ALWAYS not shiftet, but the next peak at 13.55min is shifted at 13.65 (0.15min shift)


Is the GC getting enough carrier gas pressure to maintain the set flowrate when the oven heats up?

I'd figure out what the max injection port pressure is that the method needs. Then set the inj port pressure a bit higher than that, and make sure it can reach that setpoint.


It is a column flow constant method. The flow is 1mL/min in all the chromatogram and no trouble exist in the flow.
CrisTheChemist wrote:
MichaelVW wrote:
CrisTheChemist wrote:
peak at 12.0min is ALWAYS not shiftet, but the next peak at 13.55min is shifted at 13.65 (0.15min shift)


Is the GC getting enough carrier gas pressure to maintain the set flowrate when the oven heats up?

I'd figure out what the max injection port pressure is that the method needs. Then set the inj port pressure a bit higher than that, and make sure it can reach that setpoint.


It is a column flow constant method. The flow is 1mL/min in all the chromatogram and no trouble exist in the flow.


You may want to monitor the actual pressure compared to the set point during the run. We have had issues in the past when the EPC can't keep up with the pressure set point during a run causing shifts in the retention time.
Andy F wrote:
CrisTheChemist wrote:
MichaelVW wrote:

Is the GC getting enough carrier gas pressure to maintain the set flowrate when the oven heats up?

I'd figure out what the max injection port pressure is that the method needs. Then set the inj port pressure a bit higher than that, and make sure it can reach that setpoint.


It is a column flow constant method. The flow is 1mL/min in all the chromatogram and no trouble exist in the flow.


You may want to monitor the actual pressure compared to the set point during the run. We have had issues in the past when the EPC can't keep up with the pressure set point during a run causing shifts in the retention time.


Yep, me too.

I think my systems will shut off if the difference between expected and actual pressure is too high, but it allows enough leeway for it to keep running samples if it's just lagging a little bit.
While dismissing everyone else's suggestions you have solved the problem yourself; it has to to with the flow switching in the thermal desorber. My suggestions for troubleshooting it are all old and obvious, so I will leave you to it.
Peter Apps
19 posts Page 2 of 2

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