Chromatography Forum

Hi, Everyone
recently i change the mobile gas from He to N2 and makeup gas to N2 too. I also use temperature programme for my FID splitless GC. My question is when i use N2, i set up Purge time is 0.5m,the solvent peak is good, but between solvent and decane, there are lots small peaks in there as if there is comtanmination. However, when i change gas to He and purge time still is 0.5m(purge flow is 40ml/min), i have big solvent tailing.
can you explain why?
thank you very much

First question is what else are you changing besides the carrier gas - like flow rate? And what conditions are you using with each?

Second question: what column dimensions are we talking about? (Ideal flow rate differs depending on carrier gas and column dimensions.)

If you have electronic gas controls on the GC you need to change settings when you change carrier gas, otherwise all the flows will be different to what you set.

Peter