Nitrogen Carrier Gas for GC – Reduced Response Because of Slower Oven Program Rate

When you get into a discussion with Jaap de Zeeuw about gas chromatography, you better have the data to back your position.  In fact, that is one of the best things about working with Jaap.  He challenges you to get in the lab and prove your point (or his).  Not that I have to be pushed to the lab, as anyone who knows me knows that GCs are my best friends. 

Jaap mentions in his comment on my blog Nitrogen Carrier Gas for GC – Is it Feasible? – Is it Practical? that you can lose a factor of 2 in response by going to nitrogen carrier gas because of the slower program rate we use to maintain the same separation as we would get with helium and hydrogen, which are “faster” GC carrier gases.   In the case of the previous blog, the GC oven program rates were 3.5, 9, and 13.5°C/min for nitrogen, helium, and hydrogen carrier gases, respectively.  This gives factors of 2.6 and 3.9 for helium/nitrogen and hydrogen/nitrogen.   

In an experiment done for my GC training course, I looked at the effect of various program rates on the signal-to-noise values for representative organochlorine pesticides, and indeed, a decrease in response by a factor of up to 2.5 could be seen when going from 40°C/min to 5°C/min (see slide below).  Is that fatal for all analyses?  Of course not, but if we’re doing trace residue work, it is undesirable.