FID sensitivity 10X lower from different instrument

Chromatography Forum: GC Archives: FID sensitivity 10X lower from different instrument
Top of pagePrevious messageNext messageBottom of pageLink to this message  By Doug Williams on Monday, December 22, 2003 - 09:42 am:

I used a PerkinElmer GC to run a sample. When a colleague ran the same sample on a Varian 3800 GC, she had observed one-tenth the signal. Both systems had used an external PerkinElmer TotalChrom integrator set for a 1V max signal input.

Varian literature suggests that the Varian 3800 can be set for a 1V or 10V output voltage range, but I can't seem to find any information on where that setting is made. Would it be possible if the output voltage were set for 10V on the Varian and for 1V on the PE TotalChrom software that the TotalChrom signal is attenuated by a factor of 10? How do I determine the analog output voltage setting for the Varian? Would a simple solution be to change the TotalChrom input voltage to 10V to see what happens? I would think that resulting signal would be attenuated by another factor of 10.

Are there other reasons that FIDs on different systems may have a 10-fold difference in sensitivity?

Thanks for any suggestions people may have.

Doug


Top of pagePrevious messageNext messageBottom of pageLink to this message  By mgoodwin on Wednesday, December 24, 2003 - 06:29 am:

Is the background noise on the Varian also one tenth in signal? If so, then it's the output voltage range and call PE and/or Varian tech support should you get no response here.

Otherwise, if the noise level is the same and you are actually getting reduction in sensistivity, then some other reasons for this on the FID are (though not exhaustive):

air/hydrogen flows are not correct
glass liner not deactivated
split ratios are not consistent

hope this helps you out.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Russ on Saturday, December 27, 2003 - 09:32 am:

There is also a detector range setting which I think is independent of the integrator output voltage. Although HP uses powers of 2 for FID ranging (though I think really old HP's such as the 5750 used powers of 10) my memory is that PE used powers of 10 for the range function. This goes back more years than I would care to admit, so I don't know what they are doing now. My limited experience with Varian is even more distant and I cannot remember what their FID ranging was. Obviously, if the detector range setting for one is at 100 and the other is 1000, the areas would differ by a factor of 10.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Wednesday, January 14, 2004 - 03:44 am:

Hello,
Varians 3800 has also diferent s/sl-injectors,
the discrimination in the 1079 is extremly high for split mode... the newer 1177 s/sl injector is better. adjust the column exteme exactly !

The VA FID has ranges 9,10, 11, 12. 12 is the most sensitive range = range 1 in Chrompacks GCs.


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