Flame Ionization Detector - Additional Considerations

Additional Considerations

However, one thing to note is that the FID is detecting oxidized carbon atoms in ion form. In organic species that already have oxidized carbons via the presence of oxygen, a weaker signal is given when the sample enters the detector because the oxidized carbons are not ionized as effectively as compared to compounds solely of carbon and hydrogen. Functional groups such as carbonyl, alcohol, halogens, or amines are sources of these oxidized carbons, sometimes causing few if any ions. This points out one of the main drawbacks of using an FID to detect effluent as it comes off a gas chromatograph column. Another drawback is the sample is destroyed, making it impossible to use the sample for other measurements. For this reason the FID is typically the final detector or stage in a series of instruments.

Some of the benefits of a flame ionization detector are quite useful. FIDs are insensitive to H₂O, CO₂, CS₂, SO₂, CO, NO_x, and noble gases because they are not able to be oxidized/ionized by the flame. This allows samples to be studied even if contaminated or if some leakage of ambient room gases occurs at the time of the injection. Additionally, it has the ability to determine when a sample will elute off the column with regards to the solvents used. Some detectors can be damaged if an effluent too concentrated is analyzed, making it necessary to turn it off to prevent damage. The FID is rugged, meaning that column parameters can be tested to find good separation of the constituents of a sample in the column and also from the solvent so delays can be added to more sensitive instruments to prevent damage.