Nitrogen Phosphorus Detector

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The Nitrogen Phosphorus Detector (NPD) is used in Gas Chromatography by utilizing thermal energy to ionize an analyte. With this method, Nitrogen and Phosphor can be selectively detected with a sensitivity that is 10⁴ times greater than that for Carbon (memory-hook: C, has four valence electrons,NP detection sensitivity is ten to the power of four times greater).

NP-Mode: A minimum concentration of H₂ gas is used just so that it is no longer ignitable. A rubidium pearl, which is mounted over the nozle, ignites the H2 gas (by acting catalytically), however entails the formation of a cold plasma. In this plasma the alkali atoms are excited and eject an electron which is captured by nitrile radicals, caused by the plasma. (stochastic process with the equillibrium being at the side of the nitrile radical as it features a greater electron affinity). This process creates cyanide anions, which subsequently e.g. with H-radicals by separating an electron, can form prussic acid (hydrocyanic acid). The electron is detected at a collector electrode. The created Rubidiumcations are neutralized at the negative potential of the Rb-pearl.