Make-up gas FID detector

[Loys74]

Hi!
Does someone already have result variability depending make-up gas used (He and N2) and make-up gas flow?

Thanks!

[cjm]

You may see a difference in baseline depending on the gas used. We use nitrogen makeup and set column + makeup = constant = 30 mL/min. This has always worked well for us. If using helium it may be cost effective to switch to nitrogen.

[nipe]

The construction of modern flame detectors is the same as for old FID for packed columns and relations for carrier gas/H2/air: 1:1:10 is the same also. Because total flows of FID are classic also: 30ml/min carrier (capillary column+make-up) and H2, and 300 mi/min - air. Carrier gas for column and make-up are wishing the same also.

[Peter Apps]

There is (old) literature on this. The signal:noise is better with nitrogen because its higher MW enhances the thermal fragmentation and ionisation of analyte molecules (basically they spend more time in the reaction zone at he base of the flame). Given the terrible proce of helium it makes no sense to use it instead of nitrogen as makeup.

[hcs]

Using a make N2 as make up gas increases the sensitivity by ~2 times compared to no make up gas. I have no experience with He as make up gas.