5.2.1 Analyte ionization
Analytes can be introduced into the ionization zone of a MS in two states, a solid or a vapor. Solids can be introduced by depositing milligram quantities of pure analyte onto a metal probe or in a matrix that is inserted into the ionization chamber. These more direct forms of ionization do not require the interfacing of a separatory instrument such as GC or LC since relatively pure analytes are directly placed into the MS. More commonly, analytes enter the MS system in a pure form (a peak) after separation by a capillary column GC. The MALDI technique, an increasingly popular tool described below, does not neatly fit into either of these categories but is included below due to its powerful applications for biological systems. Irrespective of the samples state, analytes must be ionizated into positively charged ions, and are in some cases broken into fragments before they can be detected. Almost every compound has a unique fragmentation pattern that can subsequently be used for conclusive identification purposes. This pattern is dependent on the type of ionization source used and the stability of the energized analyte molecule. Below we will divide the ionization techniques into those for solid, non-volatile analytes and volatile analytes entering the MS from a GC.
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