VINYL CHLORIDE different area GC-FID

Discussions about GC and other "gas phase" separation techniques.

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Hello,
I am trying to create method for vinly chloride in MeOH (GC-FID) and i did it but disturbing is that:

-with every next inj peak area of VC is lower (on the same method's parameters) for example: first inj area is about 200, next 180, next 150... FOR THE SAME CONCENTRATION. :?:
-with every next inj peak has faster RT.. it is few sec but putting 3 or 4 chromatograms on i can see it clearly.

Method is short - it has only about 7 min. I know that VC is volatile but maybe is also another reason? Have anybody any solution for that problem, colud anybody please help me? :)
Are you running purge and trap or headspace injections?
No, we unfortunately don't have headspace.. It is "normal" injection by autosampler.
So a solution of vinyl chloride in an autosampler vial injected via syringe. Vial at room temperature in the A/S rack. Each injection from a fresh vial.
Is this the procedure?
What is your column and inlet?
Yes, as you said. Every injection was from same vial - it is usually procedure and normal that every inj is done from same vial (at least in 2/3 repeats).
I could try do inj from different vials but i'm afraid of that in time from 1st inj to 20th (even from different wials) VC will disappear and the results will be false.

I use DB-WAX column (30m, 0,53mm, 1um) and inlet temp 160*C.
Vinyl chloride will escape from the vial through the punctured septum. You should have better results from separate vials. If you still see loss then you don't have a good seal or too much head space in the vials. Remember that vinyl chloride is a gas at room temp.
As Steve said, VC is very volatile and it will be lost from a punctured vial and even to headspace in a vial that sits at room temperature, and even from a vial in a freezer if not sealed completely.

To save on standards, I would use one of the small volume inserts and fill it completely to the top (about 250-300ul) that way the VC concentrations would be more stable.
The past is there to guide us into the future, not to dwell in.
The retenmtion shift may be because you are overloading the column, what is the concentration of your samples, what volume do you inject and what is the pslit ratio? Does the peak rise more slowly than it falls ?

Peter
Peter Apps
The retention shift may be because you are overloading the column, what is the concentration of your samples, what volume do you inject and what is the split ratio? Does the peak rise more slowly than it falls ?

Peter
Peter Apps
Maybe a long shot, but another thing to check with shifting retention times is to make sure that the readiness criteria is set correctly. I had an issue with a method where the run kept starting before the oven or injector or detector temperature had fully returned to the initial condition, and the result was the peak creeping backwards by regular intervals.

Also definitely recommend separate vials with inserts for each subsequent standard injection.
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