UV OPTICAL-ABSORPTION OF MATRICES USED FOR MATRIX-ASSISTED LASER DESORPTION IONIZATION/

Previous modelling of the matrix-assisted laser desorption/ionization (MALDI) process has had to rely on matrix solution optical absorptivit ies whereas the value for the solid phase is more appropriate, Absorpt ion bands are usually broader for solids than for solutions due to the higher concentration in the former, hence solution values generally o verestimate the solid absorptivity, In order to rectify this shortcomi ng, the present work reports values of the optical absorption coeffici ent (alpha) of sublimed MALDI matrix films with measured thicknesses o f 50 to 600 nm. The matrix compounds studied were ferulic acid, sinapi nic acid, alpha-cyano-4-hydroxycinnamic acid, 2,5-dihydroxybenzoic aci d, (2,5-DHB), nicotinic acid and coumarin 120. In general the films sh owed integrated cross-sections (oscillator strengths) similar to those determined by measurements on the respective solutions, Scanning elec tron microscopy of 2,5-DHB and coumarin 120 films showed them to consi st of a uniform layer of sub-micron (similar to 300 nm) crystallites.