OPTICAL-ABSORPTION OF MATRIX COMPOUNDS FOR LASER-INDUCED DESORPTION AND IONIZATION (MALDI)

Values of the optical absorption coefficient have been determined for chemically similar (C7H6O4,5 - ring structure) matrix-assisted laser d esorption/ionization (MALDI) matrices, prepared as solid-phase sublima ted thin films (100 nm-1 mu m thickness). Sublimated films were found to have multi-peaked absorption spectra with an absorption coefficient at 337 nm of between 1.66 x 10(4) cm(-1) ('poor' matrix) and 7.95 x 1 0(4) cm(-1) ('excellent' matrix [H. Ehring, M. Karas and F. Hillenkamp , Org. Mass Spectrom. 27 (1992) 472]). These measurements have allowed an investigation of the effect that the solid-phase absorption coeffi cient has on the MALDI process. A direct correlation exists between a molecule's optical absorptivity and its suitability as a matrix at tha t wavelength, i.e. efficiency in producing ions. This is exemplified b y mass spectrometric analysis which shows a dramatic improvement in th e performance of the most poorly rated 337 nm matrix when desorbed usi ng the XeCl (308 nm) laser, the molecule displaying a higher absorptio n coefficient at this wavelength.