Negative Peak with PFPD where H2S should be

[NorthernGC]

We just completed calibration of our PFPD (Varian CP3800) using hydrogen sulfide (25ppm) in air calibration standard. Peak looks fine.
We then ran several natural gas field samples and all show "negative peak" at the exact retention time of H2S.
Can anyone help explain this?

[Spuzzin]

I've seen this with highly concentrated samples, although it is usually a positive peak that drops to negative part way through then jumps to positive again. Obviously an overloading issue in my case.

My suggestion would be to run the sample diluted.

Rich

[AICMM]

NorthernGC,

I don't know the PFPD all that well but I would be suspicious of a quench (based on my discussions of FPD.) I also don't know what column so I would guess either CO2 or perhaps a large concentration of ethane as my first guess. Do you have a different column available?

Best regards,

AICMM