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Selected reaction monitoring happens after ion pass through the skimmer, right before it reaches the detector. This type of monitoring is divided into three parts, each quadrupole having a different function.

Selected reaction monitoring happens after ion pass through the skimmer, right before it reaches the detector.

This type of monitoring is divided into three parts, each quadrupole having a different function.

The first quadrupole, functions as a filter for the ions from the skimmer. It only lets precursor ions with a certain m/z into the second quadrupole.

The second quadrupole is called collision cell the precursor inos are bombarded by N₂ or Ar at 10^-3to 10^-1 Pa. This bombarded causes the precursor ions to break into fragment a phenomenon that can be called “collisionally activated dissocitation “

The fragment of the precursor ions now called product ions, are then filtered by the third quadrupole before it reaches the detector. This quadrupole could filter out certain range of m/z, or allow passage for ions with certain m/z.

Because of the increase in selectivity for the analyte of interest, the single-to-nolse ratio is improved.

The process of selected ion montoring is also called mass spectrometry / mass spectrometry (MS/MS) or tandem mass spectrometry because the process inciuded mass filtration in two of its quadrupoles .