The Nitrogen-Phosphorous Detector NPD

Heteroatom selective (for organic compounds with N or P atoms separately) more sensitive for N and P compounds than FID, as well as selective for them destructive mass-flow detector more sensitive than FID for N, more sensitive than P-FPD for P, but with less dynamic range than the FID. 

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The thermionic detector (TID), also known as the nitrogen-phosphorous detector (NPD), is based on the phenomenon that a metal anode emits positive ions when heated in a gas. It is a commonly used gas chromatographic detector for the selective determination of organic compounds containing nitrogen (N) and phosphorus (P) atoms. These include the detection of pharmaceuticals, pesticides, and environmental pollutants. The detector would appear to function as the FID however, its operation is based on a completely different principle. 

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