FID Sensitivity

[fpcwsr]

I am currently using an SRI 8610B Gas Chromatograph with an FID detector and I keep getting oddly large peaks. If I inject anything more than .8uL of a neat liquid it will max out the graph. That seems normal at least. But if I inject .2uL or .4uL, sometimes I get the .2uL peak higher than the .4uL and vice versa. I feel that this is due to the very small amount of liquid I must inject which would naturally be more affected by error. I even turned the gain down to low as I was told to do so by the user manual. Any suggestions? It makes it difficult to calibrate anything! Note that right now I have only been injecting simple organics suck as benzene.

Thanks,
FPCWSR

[chromatographer1]

Your larger injections may just be a bit broader than the smaller injections due to a factor called the 'solvent effect'. The smaller injections may be smaller in width but taller. Height is not always an indication of weight, so to speak, and of course their is always the design factor of the FID where you are probably out of linear range of the detector.

No one tries to quantitate a neat injection of a flammable liquid on a FID, not seriously anyway.

You must split or dilute the liquid in another liquid that will separate from the peak of interest if you wish to measure the peak of interest. For example diluting hexane with dodecane, or propyl benzene.

best wishes,

Rod

[thohry]

Have you checked for leaks? both at the inlet and detector ends.

[chromatographer1]

Yes, of course, if your septum is bored out from multiple injections with a needle you may be constantly leaking at the inlet. Another possible cause for inconsistency.

Some wet needle injections might be called for. Leave the needle in the injector for 10-30 seconds before removing it.

best wishes,

Rod

[fpcwsr]

I'll try that. Thank you!

FPCWSR