N2/Ar and H2/He switch for the TCD detector

[guohaiqing]

I'm using a GC (model: 5890) with a TCD detector for species concentration measurements. Since my sample contains H2, so I decide to use Ar instead of He as the carrier gas. And I flip the switch on the TCD board to the N2/Ar position for better sensitivity. However, it yields the same results as when the switch is on the H2/He position and with the Ar carrier gas. It seems to me that the switch does not make any difference. The response is too low (100 counts for 95% N2). The background noise is fluctuating between 10 counts.
When I go back and use He as the carrier gas and flip the switch to the right position. The response is reasonable (60000 counts for 95% N2). Compared to the 10 counts noise level, the background looks very smooth. The only disadvantage of this is that I cannot detect the H2 concentration.

Can anyone help me figure out the problem? I doubt the switch is damaged. But when I change another board (refurbished), it's still the same. It is very unlikely that two boards are all fault.

[chromatographer1]

I may be wrong, but the switch only changes the polarity of the detector.

And the size of the peak is dependent upon the size of your injection and the flow rate through the detector, both factors you have not informed us, as well as the temperature of the detector wire.

It does sound like you are getting a low response. Read your manual for the installation test procedure and see the checkout chromatogram and duplicate it (or not). Perhaps then you will know more about your situation.

best wishes,

Rod

[guohaiqing]

Hi Rod

I am not sure. But if the switch on the board only changes the polarity, when I just flip the switch and use the same carrier gas, I will get a reversed peak. The problem is I did not get any reversed peaks. All the peaks look the same and they are within a similar response level.

Thank you.