High RSD in headspace GC

[MestizoJoe]

I'm testing ETO which is prepared in water near 20 ppm. I've been getting high RSDs since I developed the method (~3%). Now I'm getting 4-7% RSD.

I thought that I was not crimping tight enough on the headspace vial caps, but crimping tighter didn't solve the RSD problem.

Some notes on the method:

HS oven temp 90C loop 105C transfer line 110 inlet 200C

What can be done to improve thits? Could it be as simple as replacing a gold seal and liner?

[MestizoJoe]

I need to mention also that The RSD is fine for the less volatile sample which is ethylchlorhydrin (ECH). The RSDs for ECH have been consistent and always below 5%.

I thought the caps were not crimped tight enough since only the more volatile ETO has high RSD.

[chromatographer1]

EtO is quite reactive. Are your numbers high or low?

I can see you need to have temperatures somewhat elevated for the ECH, but why the high inlet temperature? Would 120C be adequate? But then I am used to not using an inlet and I never had this issue. I never used a splitter and my results were always good when I left that variable out of the equation.

But I would replace the inlet and any other sites you might consider to be reactive.

best wishes,

Rod

[MestizoJoe]

Thanks for the reply Rod.

The numbers are correct if I take the average. I observe that after using my check standard. But they vary. I don't believe it decomposes but I may be wrong.

I'll change the liner and gold seal.

A newly realized variable that might be causing problems is the lab temp during sample prep. Been a hot few days here in the G and our HVAC system isn't too notch. I'm going to do sample prep in a better controlled environment from now on.

As for the temperatures I use in the method... When the method was developed my skills were novice. The conditions are not optimal. However during method development I saw good reproducibility.

Have a great weekend. And keep it classy Kansas City.