Role of the Solid Matrix

The role of the matrix in MALDI is analogous to that in FAB (Chap. 9.3.1). Different from FAB, MALDI matrices are generally crystalline solids of low vapor pressure in order not to be volatalized in the ion source vacuum. While basically any liquid can serve as a FAB matrix, the matrix in MALDI has to absorb light of the wavelength which is intended to be used for the experiment. [63] In UV- 

the molecules must possess a suitable chromophore because energy absorption is based on the strong absorption, and thus the resulting electronic excitation of the matrices. Therefore, the structure of UV-MALDI matrices is based on some aromatic core suitably functionalized to achieve the desired properties. 

Note It is evident that the first function of the matrix essentially is to dilute and isolate analyte molecules from each other. This occurs during solvent evaporation and concomitant formation of a solid solution. Then, upon laser irradiation, it functions as a mediator for energy absorption [42]. 

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