Wavelength dependence of UV-MALDI mass spectrometry and of direct UV-LDI-MS without matrix

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In MALDI mass spectrometry, analytical sensitivity is largely influenced by the wavelength of the excitation laser. In the 1st funding period of the research project, the UV-MALDI desorption and ionization mechanisms were for the first time investigated systematically in the wavelength range of 280-377 nm by utilizing a selected set of matrix systems and peptides as analytes. These results showed that analytical performance can be substantially enhanced by adjusting the laser wavelength to the individual peak absorption of matrices. The 2nd funding period will build on these results in several important aspects. Established MALDI matrices and the analyte classes for which they are utilized will be comprehensively characterized with respect to the potential for improvement. Optimized matrix-wavelength systems that offer improved analytical sensitivity will be applied to spatially-resolved tissue imaging MS (MALDI-MSI). Next to standard matrices, liquid matrix systems that allow the generation of highly charged peptide ions will be characterized. Extension of the wavelength range to 213-450 nm furthermore allows to explore novel analytical possibilities, among which are, for example, the analysis of small molecules by matrix-free UV-LDI-MS and the UV-LDI-MSI analysis of metabolites in tissue. The studies will also deepen our knowledge about the basic MALDI mechanisms.