Similar to a Flame Ionization Detector, a NPD uses a Hydrogen/Air flame through which the sample is passed. However a NPD uses a rubidium or caesium chloride alkali bead which is heated by a coil, over which the carrier gas mixed with Hydrogen passes. The hot bead emits electrons by thermionic emissions which are collected at the anode and provides the background current. When a component that contains nitrogen or phosphorous exits the column, the partially combusted nitrogen and phosphorous materials are adsorbed on the surface of the bead. This then increases the emission of electrons and the current which is then measured.