Agilent 8890 baseline drop

The problem is as follows: Agilent 8890 is used for the investigation of total hydrocarbon index in water by the method similar to the ISO 9377-2 standard. During the run baseline signal suddenly falls and then slowly rises back to “pre-fall” level. Oven temperature at the first ramp of this method increases from 50°C to 320°C at 10°C/min rate, and the baseline drop occurs when the temperature is in 220-250°C range (Figure 1). While investigating FID signal with no injection and increasing oven heating, baseline is behaving normally at temperature range 50-220°C, but when oven temperature is around 220-250°C periodic signal fluctuations are visible (Figure 2).

The column that is used: Agilent 1223-5731 (J&W DB-5ht GC column, 30 m, 0.32 mm, 0.10 μm, 7 inch cage), carrier gas – hydrogen, detector – FID.

In order to deal with the problem o-ring and septa replacement was done, gas tubes checked for leaks and detector was washed as well, the problem still exists.

The question is how to deal with this issue.

Thank you!

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