Negative peak with FID

Chromatography Forum: GC Archives: Negative peak with FID
Top of pagePrevious messageNext messageBottom of pageLink to this message  By cecile on Tuesday, July 13, 2004 - 07:32 pm:

Hi everyone!

I am using a GC set up with capillary column, nickel catalyst and FID detector to detect CH4 and CO2.

I inject manually (syringe) the samples into the GC. They are samples from an atmosphere in equilibrium with sea water.

I got a negative peak followed immediatly by a positive one (image in a mirror) just before the CH4 peak at about 2min time. It doesn't change with the volume injected and I get it as well if I use tap water or superQ instead of sea water.

Doesn't appear with calibration gas mixture.

Does anyone have an idea what could it be???

Cheers
cecile


Top of pagePrevious messageNext messageBottom of pageLink to this message  By jay on Thursday, July 15, 2004 - 10:47 pm:

Generally I have seen negative deep anything injected with GSV or even some times GAS injected with manual injection (syring ) may be due to flow disturbance which reflect as a negative peak.
some times if carrier gas is HE & calmix may be in He so you may not get-ve peak while your sample contain N2, moisture.

Considering your dought in calibration mix no -ve peak reason may be concentration of calmix is high may be -ve peak is there just lower the scale .

This _ve peak really affects your integration ? change flow .

jay


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