We have a HP5890 Series II with electronic pressure control and ECD detectors. Our current method uses a 2ul (autosampler) injection amount, 220 degree injector temp, double gooseneck liner, programmed temperature run, and a detector temperature of 300 degrees.
What we are experiencing is retention time shifts (.10 - .20 min) which seem to be most prevalent during the morning to early afternoon. Later runs tend to stabilize and the shift is very slight (.03 min). The temperature of the room can vary from 65 degrees to as high as 80 degrees depending on the volume of samples and how many GC's or other heat generating equipment we are operating. We do not know how much the room temp varies during overnight runs.
We feel like the room temperature could be the culprit, but we also have some difficulty comprehending how a 15 degree farenheit room temperature change could have an effect on a piece of equipment with heated zones at the level the GC has. Is this normal? Technicians we have talked to inevitably begin with having us look for leaks, but we have triple checked for leaks, and besides, the shift isn't there during night runs.
Any assistance is greatly appreciated.
By Anonymous on Friday, October 10, 2003 - 10:43 am:
Your sample solvents are in the ambient air and the pressure within the vials can affect the amount of liquid stays in the needle when exposed to the ambient pressure.
Observe and take notes.
I believe you will find the problem with the sampling from the vials at different temperatures.
It is not a GC problem but an autosampler problem.
I know of similar experiences.