Home > Chemical > Technology > Sensors > Flame Ionization Detection (FID)

A flame ionization detector operates on the principle that combustible chemicals produce ions during combustion.  These ions can be detected as a current. In practice, a target gas stream is directed into a flame (typically a hydrogen-air flame) which results in the combustion of target chemicals and the production of positively charged ions and electrons. The resulting current is sensed by electrodes placed close to the flame. FID is often used as a detector following gas chromatography separations, but is also used as stand-alone instrumentation in gas monitoring applications.  Used alone, while very sensitive, FID is non-specific and produces a signal for most hydrocarbon gases. Most stand-alone FID instruments are portable or handheld configurations.    The technology is mature and FIDs have been in wide use for gas sensing for over 50 years.  Instruments are available ranging in price from $5,000 - $50,000.

What Does FID Measure?

Organics: compounds containing Carbon (C) atoms. These include:

  • Aromatics - compounds containing a benzene ring including: benzene, toluene, ethyl benzene and xylene.

  • Ketones & Aldehydes - compounds with a C=O bond including: acetone, methyl ethyl ketone (MEK) and acetaldehyde.

  • Amines & Amides - Carbon compounds containing nitrogen, like diethylamine.

  • Chlorinated/halogenated hydrocarbons

  • trichloroethylene (TCE)

  • perchloroethylene (PERC) and Freons can cause problems because the halogen released in combustion can damage the FID sensor

  • Sulfur compounds mercaptans, sulfides

  • Unsaturated hydrocarbons like butadiene and isobutylene

  • Alcohol’s- isopropanol (IPA), ethanol, methanol

  • Saturated hydrocarbons

  • butane, octane, methane, propane, ethane 

What FIDs Do Not Measure

Inorganics: Compounds without Carbon cannot be burned and cannot be detected with FID

  • Air - N2 O2 H2O

  • Toxics w/o Carbon - HCN, SO2 Cl2

  • Acids - HCl, HF, HNO3

  • Others - Ozone O3