Chromatography Forum

I'm trying to convert helium carrier to hydrogen carrier due to the explosion of helium prices. I have 2 Agilent 6890 GCs with same type column and TCD detector. I analyze hydrocarbons pesticides mostly. What I am seeing after maintenance on both to eliminate a split ratio error on either.... is that my GC on hydrogen on the TCD is less sensitive on very small peaks.
QUESTION: Is this lack of sensitivity due to using hydrogen on a TCD detector - or is one of my TCD detectors for some reason not as sensitive as the other using identical parameters? I am injecting the same test mix and I am using the best van Deemter flows for both helium and hydrogen (which yields very similar HTEP separation abilities.

TC is concentration dependent. So, I would suspect you are using a bit more hydrogen flow than you were helium flow but I cannot say for sure. I would suggest going back to the helium ml/min and just use that same value for H2 without worrying too much yet about van Deemter and see what that does.

Not clear from your post is if one GC is better than the other.

And yes, H2 has a slightly different TC than helium but if it were me that is not where I would start.

Best regards,

AICMM