Nitrogen–phosphorus detector: Difference between revisions

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The Nitrogen Phosphorus Detector (NPD) is a form of gas chromatography in which thermal energy is used to ionize an analyte. With this method, nitrogen and phosphorus can be selectively detected with a sensitivity that is 10⁴ times greater than that for carbon. NP-Mode: A minimum concentration of hydrogen gas is used such that it is just below the minimum required for ignition. A rubidium or caesium bead, which is mounted over the nozzle, ignites the hydrogen (by acting catalytically), and entails the formation of a cold plasma. Excitation of the alkali metal results in ejection of electrons, which in turn is detected by current flow between an anode and cathode in the chamber. In the presence of nitrogen or phosphorus combustion products exiting the column, the work function of the metal is reduced, resulting in an increase in the current measured.

Since the alkali metal bead is over time consumed, it must be regularly replaced - a disadvantage compared to the related FID detector which lacks the selectivity for nitrogen and phosphorus.

External Links

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-The '''Nitrogen Phosphorus Detector''' (NPD) is a form of [[Gas Chromatography]] in which [[thermal energy]] is used to [[ionize]] an [[analyte]]. With this [[method]], [[Nitrogen]] and [[Phosphor]] can be selectively detected with a [[sensitivity]] that is 10<sup>4</sup> times greater than that for [[Carbon]].
+The '''Nitrogen Phosphorus Detector''' (NPD) is a form of [[gas chromatography]] in which [[thermal energy]] is used to [[ionize]] an [[analyte]]. With this [[method]], [[nitrogen]] and [[phosphorus]] can be selectively detected with a [[sensitivity]] that is 10<sup>4</sup> times greater than that for [[carbon]].
-NP-Mode: A minimum concentration of H<sub>2</sub> gas is used just so that it is no longer ignitable. A [[rubidium]] pearl, which is mounted over the [[nozzle]], ignites the H<sub>2</sub> gas (by acting catalytically), however entails the formation of a [[cold plasma]]. In this [[Plasma (physics)|plasma]] the [[alkali]] atoms are [[excited]] and eject an [[electron]] which is captured by nitrile radicals, caused by the plasma. ([[stochastic]] process with the [[Dynamic equilibrium|equilibrium]] being at the side of the nitrile radical as it features a greater electron affinity). This process creates [[cyanide anion]], 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.
+NP-Mode: A minimum concentration of [[hydrogen]] gas is used such that it is just below the minimum required for ignition. A [[rubidium]] or [[caesium]] bead, which is mounted over the [[nozzle]], ignites the hydrogen (by acting catalytically), and entails the formation of a [[cold plasma]]. [[Excitation]] of the alkali metal results in ejection of electrons, which in turn is detected by current flow between an [[anode]] and [[cathode]] in the chamber. In the presence of nitrogen or phosphorus combustion products exiting the column, the [[work function]] of the metal is reduced, resulting in an increase in the current measured.
+Since the alkali metal bead is over time consumed, it must be regularly replaced - a disadvantage compared to the related [[Flame ionization detector|FID detector]] which lacks the selectivity for nitrogen and phosphorus.
+==External Links==
+[http://www.chromatography-online.org/GC/Detectors/Nitrogen-Phosphorus-(NPD)/rs39.html]
 [[Category:Gas chromatography]]