Chromatography Forum

We are trying to put back together a 15 year old Shimadzu 17a gas chromotography. (It was still being used 2 years ago). We want to use it to measure hydrogen so we are using argon as a carrier and nitrogen as a make-up gas. When we try to run a test sample of just air, we get an alarm that says "TCD current overload". Has anybody ever seen anything like this, and do you know how to fix it?

I don't know if this is related, but every once and a while we also get a error that says there is a leak in the carrier gas. We have tested the inlet lines to the GC and they are OK, and we are using an autosampler so I'm under the impression that we don't need to worry about the septum going bad on us.

FYI- A technician came out and told me this meant the TCD was busted.

Sounds like the TCD filament current was too high. You can put it higher in hydrogen and helium than nitrogen and argon as the thermal conductivity is higher in H2 and He. This could be why it's broekn now. Also some instruments say "leak!" when you get a large air/argon etc. peak using helium carrier, it's not really a leak but appears to be - this is an auto shut-off to prevent filament damage. Sounds like that was the error you were seeing.

Hi

In each Shimadzu TCD manual you'll find a graph with curves showing maximum current you can set depending on detector temperature and kind of carrier gas you use.

For GC-17 TCD and for N2 carrier gas current should be not bigger than 50mA. So I suppose for Ar even less.