Small-molecule MALDI using the matrix suppression effect to reduce or eliminate matrix background interferences.

The matrix suppression effect (MSE) can lead to high-quality MALDI mass spectra: strong analyte signals and weak or negligible matrix background peaks. Experiment and theory suggest that MSE should be widespread and, therefore, generally applicable to measurement of low molecular weight (LMW) substances. These are otherwise impractical with MALDI due to interference from matrix. Appropriate conditions for MSE were investigated and tested on a variety of LMW substances. Straightforward and semiautomated interpretation was possible for 87.7% of these. Another 3.5% gave poor MSE due to sodium cationization rather than protonation of the analyte, but interpretation was possible. MALDI imaging shows that MSE varies significantly across a typical sample. Selective data accumulation could further increase the utility of the method. Samples containing more than one analyte were also studied. Analyte-analyte suppression was not found to be excessive, and moderately abundant minority species can be adequately detected.