Tandem mass spectrometry scan type

Superior sensitivity, efficiency, and specificity have made high-performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS), the predominant analytical technique for characterization and quantitative analysis of metabolites (Kostiainen et al., 2003 Ma et al., 2006 Prakash et al., 2007). Ion trap, triple-quadrupole, and quadmpole time-of-flight (Q-TOF) mass spectrometers are routinely used to profile and characterize metabolites in plasma and excreta (Ma et al., 2006). The combination of scan types and features available on mass spectrometers of different design (product ion, MS", neutral loss, precursor ion scans, accurate mass measurements) allows identification and characterization of putative and unexpected metabolites with or without little prior knowledge of biotransformation pathways of a given dmg molecule. 

Another technological development in tandem mass spectrometry is the combination of two TOP mass spectrometers, TOF/TOK These instruments have excellent sensitivity and throughput for MALDI-MS/MS and are especially suited for proteomics research. However, these instruments are unable to perform true precursor ion scans or constant neutral loss scans. The Bruker Daltonics ultra-flex and Applied Biosystem 4700 proteomics analyzer are examples of this type of instrument, Such mstruments have yet to make an impact in clinical chemistry. 

Magnetic analyzers are often used in various combinations with electrostatic sectors. Sector instruments are characterized by good ion transmission. Depending on the order of these analyzers, very high resolution and wide mass ranges can be achieved. Sector instruments suffer from a relatively low scan rate, which makes their application in GC-MS and LC-MS studies somewhat limited. At the same time, some types of tandem mass spectrometry experiments with mass-selected ions can be performed only on this type of equipment. 

Alternatively, the primary ions may be scanned with the second mass analyzer held constant to produce a parent spectrum. This type of tandem mass spectrometry reveals all the reactant ions giving rise to a particular fragment ion. Kon-drat et al. (215) have demonstrated applications of this technique to the identification of biosynthetically related natural products that fragment to a common ion. 

Cardoso, A.M., Barros, C.M.F., Correia, A.J.F., Cortez, A., Carvalho, F., and Baldaia, L. (1997) Identification of vertebrate type steroid hormones in the shrimp Penaeus japorUcus by tandem mass spectrometry and sequential product ion scanning. /. Am. Soc. Mass Spectrom., 8, 365-370. 

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