Flame ionization detector

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A flame ionization detector (FID) is a type of detector used in gas chromatography.

[edit] Principle

An FID is an ion detector which uses an air-hydrogen flame to produce ions. As components elute from the GC's column they pass through the flame and are burned, producing ions. The ions produce an electric current, which is the signal output of the detector. The greater the concentration of the component, the more ions are produced, and the greater the current.

[edit] Application

FIDs essentially can only detect components which can be burned. Other components may be ionized by simply passing through the FIDs flame, but they tend not to create enough signal to rise above the noise of the detector.

This selectivity can be a problem or an advantage. For example, and FID is excellent for detecting methane in nitrogen, since it would respond to the methane but not to the nitrogen.

FIDs are best for detecting hydrocarbons, and other easily flammable components. They are very sensitive to these components, and response tends to be linear across a wide range of concentrations.

However, FIDs destroy the components they are detecting. For example, with a TCD the components can continue on to another detector after passing through the TCD. (This can be useful for analyzing complex mixtures where different detectors are needed because of differing detector selectivities.) However, with an FID, the components are destroyed and no further detection is possible.

For this reason, in multiple-detector situations, the FID is always the last detector.

[edit] External links

• Library 4 Science Further Chromatography Reading
• Chrom Forum Discussion forum for chromatography; has a "Student Projects" section for beginner's questions