INVESTIGATIONS OF 2,5-DHB AND SUCCINIC ACID AS MATRICES FOR IR AND UVMALDI - PART-I - UV AND IR LASER-ABLATION IN THE MALDI PROCESS

UV and IR laser ablation under MALDI conditions is described for two t ypical solid UV and IR matrices. 2,5-Dihydroxy benzoic acid (2,5-DHB) as a UV and IR matrix and succinic acid (SA) as an IR matrix were inve stigated systematically by light and electron microscopy, and by mass spectrometry. Large single crystals of 2,5-DHB and SA with and without protein incorporated were used for the experiments.;The UV MALDI expe riments were performed with a flat-top laser beam profile. Within a li mited fluence range, these exposures resulted in the formation of typi cal cone structures, occurring after several hundred laser shots onto a given spot. Such structures had originally been described for materi als processing of polymers and ceramics with excimer lasers. For the I R exposures, a Gaussian laser beam profile was used. The much lower ab sorption of matrix compounds at IR wavelengths compared with the absor ption of matrix compounds at UV wavelengths results in a much larger p enetration depth of the IR laser light into the matrix solid and conse quently in a much higher ablation depth and amount of ablated material . This large volume of material, ablated per single exposure, prevents the formation of specific surface structures in IR MALDI. The amount of matrix material ablated per laser shot was measured with a laser pr ofilometer to about 10000 mu m(3). This determines the amount of consu med protein per laser shot to about 1 fmol under typical IR MALDI cond itions. (C) 1997 Elsevier Science B.V.