Chromatography Forum

Hi guys,

I'm unable to get a flat TCD baseline; it drifts wildly as I change oven temperature. If I increase the oven temperature the TCD signal decreases and eventually recovers to a slightly lower steady-state value. If I decrease the oven temperature, the TCD signal increases and then recovers partially.

I have leak tested the entire system using Agilent's pressure-drop method and using an electronic leak detector, and no leaks are present. Agilent came to service the instrument and switched out the entire purged packet inlet, my packed column, and even the EPC module. One hefty bill later, the problem has not improved at all.

Haefa

This is one of the disadvantages of a TCD. You can get around this problem by using the column compensation on the GC. This records a baseline over the entire temperature program without an injection. If this baseline is reproducible, its is subtracted from your chromatogram, a you get a chromatogram with a flat baseline.

TCD's will often change baseline with oven program. Lots to explain about that. However, the line that caught my attention was the direction of the drift. Usually, my experience is higher oven, more baseline. So.... what carrier are you using, what column and what oven parameters? Supposedly the Agilent tick tick detector would minimize drift but I have not seen that to be the case.

Did it ever not move up and down on oven program?

Best regards,

The TCD works similar to the electronic leak detectors as it measures the conductivity of the gas flowing through it. The TCD also should have a reference flow of the same gas as the carrier. If there are any differences in the flow between the two, then you can get shifts in the baseline.