Help with the term Injection plug width
Posted: Tue Apr 12, 2022 8:14 am
by studentjelena
Hello!
I can't find any simple explanation what is injection plug width and how does it effect my results. I am working on headspace GC FID and found the term ''injection plug width'' linked to repeatability issue of my peak areas that I am experiencing.
Re: Help with the term Injection plug width
Posted: Mon May 09, 2022 3:18 pm
by rb6banjo
I have never heard/read that term before. I've been at this stuff for 30+ years.
Perhaps they mean the sample volume?
Some headspace units employ a fixed-volume loop on a rotary injection valve to get the sample in the GC. The vial is pressurized slightly (external gas or elevation of the vapor pressure in the vial by heating) to force-fill the loop. The pressure in the loop is allowed to vent to atmospheric pressure and then the injection is made when the valve turns and the carrier gas sweeps through the loop.
Others increase the pressure in the vial and allow the pressure to vent into the transfer line for a fixed amount of time to make the injection.
As with all gas chromatography, you'd like the analytes in your sample volume to condense at the head of the column to get the best chromatography and separations. If they don't they'll smear and your peak shapes for those analytes will stink.