carrier gas

[edmgc7788]

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

[Don_Hilton]

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.)

[Peter Apps]

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