The TCD detector on our 6890 Gc shows negative peaks for water acetylene , propadiene .

We have a Gc (6890) with TCD . The Gc & the method setup has been around for years . It measures some permanent gases & some Hydrocarbons .


The method starts with negative polarity to detect H2 (He is the carrier ) & then the polarity is switched to detect N2, O2, Ar, CO, CO2 ,H2S, methane , ethylene , acetylene , propane , propylene , butanes , pentanes


Off lately the TCD is giving us issues . It shows negative peaks for acetylene , propadiene, water  sometimes H2S.


These peaks never used to be negative . This is a new TCD ( changed in Oct 2020). We had similar issues with previous TCD So we had to change it .I am not sure why we have started seeing this negative peaks .

We never had this issue before


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