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 desorption/ionization (MALDI) matrices, prepared as solid-phase sublimated thin films (100 nm–1 μm thickness). Sublimated films were found to have multi-peaked absorption spectra with an absorption coefficient at 337 nm of between 1.66×104 cm−1 (`poorʹ matrix) and 7.95×104 cm−1 (`excellentʹ 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 coefficient has on the MALDI process. A direct correlation exists between a moleculeʹs optical absorptivity and its suitability as a matrix at that wavelength, i.e. efficiency in producing ions. This is exemplified by mass spectrometric analysis which shows a dramatic improvement in the performance of the most poorly rated 337 nm matrix when desorbed using the XeCl (308 nm) laser, the molecule displaying a higher absorption coefficient at this wavelength.