Ketone response doubling periodically.

[kellerc2]

My volatiles GC/MS will periodically have doubled response for all of my ketones while all other QC is in, ever hear of this problem?
Cory

[rb6banjo]

What is your injection technique?

[kellerc2]

Purge and trap.

[James_Ball]

Is your room temperature relatively stable? Ketones respond well to warming of the sample when purging. Also purge flow makes a big difference in Ketone response while other compounds will remain about the same.

I have gone months with normal responses then seen them either go very high or very low. The good thing is Ketones don't stick around in the purge and trap so even extremely high samples will flush out quickly. Carbon disulfide and tetrachloroethene on the other hand will hang around for weeks if you get hammered with a bad sample.

If you have a way to do heated sparges, try running your sparge tube at about 40C while purging and see if that helps make them more stable.

[Yama001]

James is correct regarding room temp fluctuation; also be aware you if start off with relatively cool water fresh from the tap/filter - the first standard you purge may have a lower response than subsequent runs as the water temperature equilibrates.