Investigations of 2,5-DHB and succinic acid as matrices for IR and UV MALDI. Part: I UV and IR laser ablation in the MALDI process

Abstract

UV and IR laser ablation under MALDI conditions is described for two typical 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 investigated 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 experiments were performed with a flat-top laser beam profile. Within a limited fluence range, these exposures resulted in the formation of typical cone structures, occurring after several hundred laser shots onto a given spot. Such structures had originally been described for materials processing of polymers and ceramics with excimer lasers. For the IR exposures, a Gaussian laser beam profile was used. The much lower absorption of matrix compounds at IR wavelengths compared with the absorption of matrix compounds at UV wavelengths results in a much larger penetration depth of the IR laser light into the matrix solid and consequently 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 profilometer to about 10 000 μm 3. This determines the amount of consumed protein per laser shot to about 1 fmol under typical IR MALDI conditions.