Chromatography Forum

I have a large peak at the beginning of my GCMS chromatograms. I am running 5973/6890 with a Tekmar PT and Stratum. I thought it was a solvent peak, but it's there when I just run water through - it does magnify when MeOH is added to the sample. I am trying to run 524.2, but this peak is covering my first 6 compounds.
I'm running a DB-VRX (30x0.25)
Initial temp of 40 (4.00min hold), increase 10deg/min to 180, increase 15deg/min to 225 (hold 1.0min)

Does anybody have any suggestions on how to get rid of this peak? I'm fine with a solvent peak, but this one is overlapping my analytes of interest.

Thanks!

First step - get an MS spectrum of the large peak and identify what chemical it is.

Peter

My money's on CO2. I always see it in purged water samples. The spectrum is mostly 44 correct?
Nothing you can do except increase your solvent delay time ( if you can), or learn to live with it.
I do not currently see it now using a 0.18 column. I would recommend your switching to a 20M X 0.18 X 1.0 column for your application. You can reduce the amount of water getting to the source ( belive me it causes problems).
Also ignore what Tekmar says and use a Vocarb 3000 trap ( you can get them directly from Supelco now).
Also try to limit the amount of MeOH you purge with carbon based traps, they don't trap as much MeOH but do a very good job of foccusing what they trap!

If it is CO2, set your MS to scan from 45 m/z on up until just before acetone. Then at least you won't have to look at it.

It is mostly CO2! Also, I am using a Vocarb 3000. I pulled out the GC uinlet last night - it was VERY dirty, didn't know if that would make a difference. I will try running some blanks on it today and see what they look like. I will also look into getting a smaller diameter column.
Won't I lose some of the lighter compounds if I set my MS scan to start at 45m/z?

THANKS!

The lowest ion I have before acetone is 45 for a qualifier for diethylether.
Acetone needs to go lower, 43 m/z, so you have to change your scan before you get there. I include Freon 113 so I scan from 45 to 200 for the first segment.

Try starting temp of 35C. I use that and my gases come out after the CO2.

Hi
I writing from Mongolia.
I have same problem with my chromatogramma.
Pls write me how to resolved your problem.
My english is too bad sorry kkk.
and send me your data acquisition method.
TNX