Baseline dip at high temperatures

[derekino]

I have been having a problem with my baseline starting high after the air peak then difting down even lower than my baseline. Then after the method is complete the baseline returns to normal. I only noticed this after switching to high sensitivity mode on the TCD. Any suggestions?

[aldehyde]

What carrier gas, what make up gas, what analyte/sample matrix?

[derekino]

We have two 5890s that we have manufactured our own headspace analyzer for. We use helium as our carrier gas and have bypassed the purge system. They have been setup like this for decades, but lately just one of them has started to exhibit this baseline dip. The samples we test are small round punchouts of coated material for retained solvents. Usually MEK, Toluene, alcohols etc.