Tandem Mass Spectrometry

Of the ionization techniques described, only the particle beam method produces sufficient fragmentation to give structural information. The softer ionization methods allow for RMM determination from either protonated molecule ions and/or adduct species, with little or no structural information being available owing to lack of fragmentation. It is possible to induce some degree of fragmentation in both thermospray and API sources by manipulating the source conditions. A more specific means of promoting fragmentation involves the use of sequential mass analysis, i.e. the isolation of a precursor ion followed by its interaction with a target gas to induce fragmentation by collisional activation, thus allowing a product ion mass spectrum to be recorded. This and other types of CID experiments can be carried out in time, in an ion storage device or in space using scanning or time-offlight instruments. For a full discussion of the instruments and experiments possible, the reader is referred to the Further Reading section.

The most commonly used type of tandem mass spectrometer is the triple quadrupole, and benchtop instruments of this type with a dedicated LC interface are commercially available. They are relatively easy to use and offer a range of MS-MS scans. In addition to the product ion scan and the reaction monitoring scan (both MS1 and MS2 operate in selected ion mode), two other scan modes are available - precursor ion and constant neutral loss. In the former, MS1 is scanned whilst MS2 is set to pass a specific ion, thus yielding information as to the origins of a specific fragment ion. This may be employed to identify those components of a mixture which contain a common functional group, e.g. sulfonated compounds will typically fragment to give an ion at m/z 80 (SO3) in negative ion mode; thus a precursor ion scan of this ion should be specific for the presence of sulfonates. Neutral loss scans involve scanning both MS1 and MS2, but with the respective mass ranges offset by the mass of the neutral species.

Solar Panel Basics

Solar Panel Basics

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