FID Baseline Drops

Chromatography Forum: GC Archives: FID Baseline Drops
Top of pagePrevious messageNext messageBottom of pageLink to this message  By Dean Thome on Thursday, January 10, 2002 - 07:17 am:

I am new to using a GC and our lab has an old HP 5710A with an FID detector. I've gotten it up and running but the baseline periodically experiences sudden drops (downward spikes of approximately 4 mv). This is hampering the ability of the Millenium 32 software to accurately determine peak areas. What could be causing such a problem?


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Friday, January 11, 2002 - 02:46 am:

We experienced similar negative peaks on one of our instruments and traced the problem back to a faulty gas regulator...in our case it was a faulty electronic pressure controller, but since you are using an old GC, your problem may be a faulty gas regulator. You did not say what gas you are using, but we experienced that irregular flow is more prominent when using hydrogen as a carrier. With helium the problem still persisted, but to a lesser degree.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Bruce Freeman on Tuesday, January 15, 2002 - 11:52 am:

We used to have a strange problem like this on old HP5890 GC's. In that case, the baseline dropped to zero and stayed there about 1/2 second, then recovered like nothing had happened.

Eventually I correlated it to touching the top of the instrument. HP added a grounding strap between the top (metal, ungrounded) cover and the chassis of the instrument, and we never saw tha problem again.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Beppe on Wednesday, January 16, 2002 - 12:02 am:

We had exactly the same situation as Bruce (and the same solution).
Note that the phenomenon was depending on the individual touching the instrument (or maybe on the condictivity of his shoes ... !)


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