Electron capture detector

The electron capture detector (ECD) was invented in 1957, by Dr. James E. Lovelock .^[1] It is a device for use in gas chromatography that can detect tiny amounts of chemical compounds in the atmosphere and elsewhere. The electron capture detector is used in detecting electron-absorbing components in the output stream of a gas chromatograph. The ECD uses a radioactive Beta particle (electrons) emitter -- a typical source contains a metal foil holding 10 millicuries of Nickel-63. The electrons formed are attracted to a positively charged anode, generating a steady current. As the sample is carried into the detector by a stream of nitrogen or a 5% methane, 95% argon mixture, analyte molecules capture the electrons and reduce the current between the collector anode and a cathode. The analyte concentration is thus proportional to the degree of electron capture, and this detector is particularly sensitive to halogens, organometallic compounds, nitriles, or nitro compounds.

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Sensitivity

The ECD is 10-1000 times more sensitive than an FID, and one million times more sensitive than a TCD, but has a limited dynamic range and finds its greatest application in analysis of halogenated compounds. The detection limit for electron capture detectors is 5 femtograms per second (fg/s), and the detector commonly exhibits a 10,000-fold linear range. This made it possible to detect halogenated compounds such as pesticides and CFCs, even at levels of only one part per trillion (ppt), thus revolutionizing our understanding of the atmosphere and pollutants.

References

Reviews

• M. Krejči and M. Dressler (1970). "Selective detectors in gas chromatography". Chromatographic Reviews 13 (1): 1-59. doi:10.1016/0009-5907(70)80005-9.
• E. D. Pellizzari (1974). "Electron capture detection in gas chromatography". Journal of Chromatography A 98 (2): 323-361. doi:10.1016/S0021-9673(00)92077-6.
• J.E. Lovelock (1974). "The electron capture detector". Journal of Chromatography A 99 (1): 3-12. doi:10.1016/S0021-9673(00)90840-9.