Nitrogen-phosphorus detector

The nitrogen-phosphorus detector ( nitrogen phosphorus detector , NPD, and PND) is one of the selective detectors . Compounds that contain nitrogen or phosphorus or have an odd number of electrons are detected. The structure is similar to the flame ionization detector (FID).

With the NPD, the sample is passed through a hydrogen / air plasma without the hydrocarbons being ionized to any great extent. There is a heated ceramic bead (usually made of rubidium or cesium silicate) above the nozzle. Alkali ions on the ceramic bead and an appropriately selected temperature enable the selective ionization of nitrogen or phosphorus compounds. A current flows that is proportional to the amount of ions generated.