A fast atom bombardment and matrix‐assisted laser desorption/ionization mass spectrometry study of doubly charged porphyrins

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Abstract
In this mass spectrometry (MS) study of doubly charged porphyrin salts, fast atom bombardment (FAB) and matrix‐assisted laser desorption/ionization (MALDI) MS techniques are utilized to examine several unique ionic species. The predominant transformation of preformed doubly charged ions in the desorption/ionization mechanism of FAB and MALDI is the result of deprotonation reactions to form singly charged ions of the type [M2+ − H+]+ and of one‐electron reductions to form radical cations [M2+ + e−]+·. The dependence of this phenomenon and the formation of a number of additional ionic species on the different matrices and the FAB‐matrix additive benzoquinone is examined. The significant analogous behavior of doubly charged porphyrins in FAB‐ and MALDI‐MS leads to the conclusion that one‐electron reductions are of distinct relevance in the desorption/ionization mechanism of MALDI. Copyright © 2001 John Wiley & Sons, Ltd.