Chromatography Forum

Hi everyone,

GC : Agilent 6890 with TCD detector (helium carrier gas)

I'm currently having an issue with my H2 peak. Since I'm using helium as carrier gas, I use negative polarity to get my H2 peak. The GC was running fine until recently. All of a sudden, I get a negative hydrogen peak with negative polarity. It becomes split (combination of positive and negative) as I increase the H2 concentration. I've checked with 2 different columns (ShinCarbonST and Hayesep DB), and both of them have this problem. (Both of them were working fine before)

The only thing that I've changed recently is the helium cylinder. Do you think impurities in the cylinder can cause this problem? Or is the problem with my TCD detector?

Any suggestions/insights will be greatly appreciated

msakbo01

I would not use helium as carrier gas for hydrogen analysis at concentrations below 15% H2. The results are what you are seeing and are due to laws of physics, not a defective detector. For good results, use nitrogen or argon as carrier gas.

Gasman

Agree with Gasman on this one too. Split positive/negative peaks on TCD while analyzing H2 with He carrier is very common. You say it was working previously -- that is either luck or higher H2 concentrations or you just didn't notice before. In any case, linearity is horrible and so unless your standard had the same exact composition as your samples, any results were meaningless.