I am running gas samples through our TCD on our 8890 GC. Recently, the helium carrier gas tank was replaced, and the average area count of air from a calibration gas standard decreased from around 290 to 220 after this replacement. The peak height decreased by about 20%
Running at 45C column temperature, 200C detector temperature at a flow rate of 8.2mL/min
I tried running UHP helium through the detector and at the retention time for air there is now a negative peak which wasn't present before. Does anyone have suggestions on troubleshooting or what the cause is for this negative peak? I believe this is the reason for the measured magnitude of the air from the cal gas decreasing.
