Matrix Properties in Selective Ionization by MALDI

Selection of a suitable matrix to analyze a particular lipid class or a category of lipid classes is important for MALDI-MS analysis of lipids and has been well documented [54-57], It is conventional to use a-cyano-4-hydroxycinnamic acid (CHCA) for analysis of lipids in the positive-ion mode while 2,5-dihydroxybenzoic acid (DHB) in the negative-ion mode. Utilization of these matrices results in some of the obstacles for quantitative and global analyses of cellular lipidomes (see Chapter 2). 

Collectively, different matrices possess their different physical properties and could match with different lipid classes in crystallization and ionization process. Appropriate selection of a matrix for ionization of a particular lipid class or a category of lipid classes could lead to ionization in high sensitivity, quantitation, and effectiveness. In addition to the mixed matrix component systems, it appears that the matrix 9-aminoacridine could provide the best ionization for global analysis of cellular lipidomes. In any case, the variation of matrices for ionization of different lipids is an important dimension in lipidomics. Furthermore, understanding the roles of matrices in selective ionization of different lipid classes, enhancing ionization sensitivity, and the resulting reproducible and quantitative data is still warranted. 

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