Detailed description of ECD

Electron capture detectors contain an electron radiation source (i.e., a -particle emitter; typically ⁶³Ni or ³H) and a pair of oppositely polarized electrodes. The emitted electrons collide with the carrier gas (a mixture of methane and argon or nitrogen) and produce plasma. The latter is a reactive gas phase that contains positive ions and thermal (i.e., low-energy) electrons. These act as charge carriers and generate a current between the cathode and the anode. Organic analytes that elute from the gas chromatography column into the detector capture thermal electrons. The resulting decrease in current is reported as a chromatographic peak.

ECDs are particularly sensitive to organic compounds with high electron capture efficiencies. This explains the high sensitivity of ECDs to compounds that contain electro-negative functional groups, such as halogen, carbonyl, and nitro groups. In fact, many chlorinated organic pollutants are typically quantified using a GC-ECD system. Furthermore, the signal intensity of the ECD is proportional to the amount (or concentration) of molecules passing through the detector over a wide concentration range. However, like FIDs, ECDs give little to no information on the structure of the eluting compound and hence cannot be used for compound identification, except simply by compound retention time.