Selective detection of target compound class

Spectrum of the ions produced by a collision-induced dissociation of the pseudomolecular ion of octanoylcamitine. This spectrum is obtained by selecting the 288 Th ion by means of the first analyser, fragmenting it through collision in the collision cell and analysing the fragments using the second spectrometer. 

We conclude that we could selectively detect the carnitine conjugates by looking for the precursors of the 85 and 144 Th fragments, or by detecting the losses of 59 or 161 Da neutrals. 

Fragmentation diagram of carnitines leading to 144 and 85 Th fragment ions, and to ions resulting from the losses of 59 and 161 Da neutrals. All these fragmentations are typical of all the carnitines, whatever the nature of the fatty acid chain R. 

This general methodology for the selective detection of compounds or compound classes can be combined with a chromatographic separation, allowing selective detection of one compound in a complex mixture. Furthermore, as already discussed at the beginning of this chapter, tandem mass spectrometry also allows the signal-to-noise ratio to be substantially improved in the detection of selected compounds or compound classes. 

The possibility to obtain both high selectivity and high sensitivity by tandem mass spectrometry is largely used in the pharmaceutical industry to monitor and quantify a selected compound in pharmacokinetics studies, which is the field that uses the largest number of tandem mass spectrometers. 

---