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purge heater issue
Posted: Wed Dec 13, 2017 5:19 pm
by wrmb041170
Our environmental lab uses a first generation Encon Evolution concentrator for VOC analysis by GC/MS. When using the purge heat option (we set it at 65C), several extraneous peaks appear early in the chromatogram. Each of the peaks exhibits the "ions at every mass" profile normally indicative of an electrical problem. I ruled out the MS, since all electrical connections checked out and cleaning the HED didn't help. Additionally these problem peaks do not occur when not using the purge heat program. Has anyone else in the field experienced this issue and can maybe shed some light on what is responsible for it?
Thanks,
Walter
Re: purge heater issue
Posted: Wed Dec 13, 2017 6:51 pm
by Bigbear
Why do you need the heater, polar compounds? I tried heated samples in the past but found all it does is introduce more water into the GC.
Re: purge heater issue
Posted: Wed Dec 13, 2017 7:14 pm
by wrmb041170
True about the extra water, but we find heating improves the purging of Ketones.
Re: purge heater issue
Posted: Sun Dec 17, 2017 4:01 am
by mckrause
Typical of an overloaded system; probably methanol or water. Since you recognize that you get a significant increase in water from heating that is where I would start.
Salt also increases the efficiency for polars and does not require heating
Re: purge heater issue
Posted: Mon Dec 18, 2017 9:36 pm
by James_Ball
We run the same instrument and set the temperature to 40C instead of 65C. It helps with recovery of ketones and alcohols but doesn't give enough problem with water that the moisture trap can't handle it.
At 40C I can easily do Acetone, 2-Butanone, 4-Methyl-2-pentanone, and 2-Hexanone down to 0.5ppb and 1,4-Dioxane down to about 10ppb.
How long is your dry purge and what trap are you using?