Electron capture detector
An electron capture detector (ECD) is a device for detecting atoms and molecules in a gas through the attachment of electrons via electron capture ionization. The device was invented in 1957 by Dr. James E. Lovelock[1][2] and is used in gas chromatography to detect trace amounts of chemical compounds in a sample.[3][4]
Gas chromatograph detector
 | This article needs attention from an expert on the subject. Please add a reason or a talk parameter to this template to explain the issue with the article. (January 2011) |
The electron capture detector is used for detecting electron-absorbing components (high electronegativity) such as halogenal compounds in the output stream of a gas chromatograph. The ECD uses a radioactive beta particle (electron) emitter, typically a metal foil holding 10 millicuries (370 MBq) of the radionuclide nickel-63. The electrons are formed by collision with nitrogen because nitrogen exhibits a low excitation energy, so it is easy to remove an electron from a nitrogen molecule. The electron is then attracted to a positively charged anode, generating a steady current. Therefore, there is always a background signal present in the chromatogram. As the sample is carried into the detector by a stream of nitrogen or a 5% methane, 95% argon mixture, analyte molecules absorb 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. ECD detectors are particularly sensitive to halogens, organometallic compounds, nitriles, or nitro compounds.
Sensitivity
Depending on the analyte, an ECD can be 10-1000 times more sensitive than a flame ionization detector (FID), and one million times more sensitive than a thermal conductivity detector (TCD). An ECD has a limited dynamic range and finds its greatest application in analysis of halogenated compounds.[5] 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
- ^ J. E. Lovelock (1958). "A sensitive detector for gas chromatography". Journal of Chromatography A. 1 (1): 35–46. doi:10.1016/S0021-9673(00)93398-3.
- ^ J.E. Lovelock (1974). "The electron capture detector". Journal of Chromatography A. 99 (1): 3–12. doi:10.1016/S0021-9673(00)90840-9.
- ^ 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.
- ^ Various. "Advisory Opinion". Innovative Technology: Gas Chromatography Field Analysis. NEWMOA Technology Review Committee. Retrieved 2011-04-21.
 | This article about analytical chemistry is a stub. You can help Wikipedia by expanding it. |