Dropping baseline during oven ramp

[calvin.poh]

I operate a Agilent GC-FID 7890B. The baseline recently has just rise to over 100. I have just replaced the jet of the FID detector but the problems still remain. Now normally at 120C oven temperature my baseline after 2-3 hours bakeout is still around 150, but during runs my baseline will suddenly drop gradually even the oven temperature is increasing. The baseline looks like going down stairs. Any suggestions on where the problem originate from? Carrier gas is hydrogen, without other markup gas, and compressed air from an air compressor. Peaks look fine, separation is good just the baseline is horrible. There is a big sliver universal gas trap before the GC.

[dblux_]

Remove FID insulation inside the oven and retight adapter nut.

[Don_Hilton]

Be sure you have no leaks around the inlet. If a leak opens with increasing oven temperature, flow thorugh the column will drop.

[AICMM]

calvin.poh,

If it were me, I would replace the split vent line and the trap. Odd, but I used to see this on the 5890's.

Best regards,

AICMM

[dblux_]

IMHO he/she is no longer interested in any advise. If after 10 days we have no feedback ...