negative peaks on tcd

[devley]

Hello everyone...any info on this would be greatly appreciated.

OK,
I have an agilent 6890. Running a packed column w/tcd. The test is an injection of itself. He is the carrier gas as well as the make/up gas. We are getting a negative peak at about the same rt as we would expect to see the solvent, but at a much smaller response...and of course negative. we have had issues like this before and found that changing the filter for He which appeared "dirty", we then installed new filter..problem solved. However the He filter is clean. The N2 filter looks bad so we changed it but obviously no changes occured seeing that the tcd and column are not being ran on N2. i have tried both a steel column and glass column, as well as changing to a different gc...and am still getting a negative peak. and to confuse me even more i am running another test also with tcd at the same time with no issues. any ideas would help!!!

[chromatographer1]

My guess is your carrier gas is not what it should be, either contaminated or the wrong gas in the right cylinder.

best wishes,

Rod

[devley]

Thanks Rod!

After I posted the question I was finally able to get some nice looking chrom by switching the gases off to the other system, normally this should not make a difference. so it may possibly be a plumbing issue. I am also going to investigate your idea as well!!! thanks soo much!

Ashley