Other important GC detectors include the thermionic detector,the electrolytic conductiviry or Hall detector, and the photoionization detector. The thermionic derector is similar in construction to the FID. Wite the thermionic detector, nitrogen-and phosphorous-containing compounds produce increased currents in a flame in which an alkali metal salt is vaporized. The thermionic detector is widely used for organo-phosphoroes pesticides and pharmaceutical compounds.