The use of salts, buffers and surfactants in LAP-MALDI MS

Biological samples such as tissue extracts and enzymatic assays typically have a complex composition, which can interfere with analyte ionisation and detection in mass spectrometry (MS). Ionisation techniques such as electrospray ionisation (ESI) are often coupled online to an upfront chromatographic separation, whereas sample preparations for techniques such as conventional matrix-assisted laser desorption/ionisation (MALDI) are performed offline and, in the case of MALDI, rely on sample clean-up owing to different crystallisation behaviour. Liquid atmospheric pressure matrix-assisted laser desorption/ionisation (LAP-MALDI) MS is a hybrid ionisation technique that has been previously used to analyse a wide range of biological samples at fast acquisition rates. Here we report data from a systematic investigation of the influence of various buffer compounds, salts, surfactants, and other compounds necessary for biological sample preparation reflected in the signal intensity of a standard peptide mixture. Tricine showed the least signal reduction from the buffer compounds tested as did octyl-β-D-glucopyranoside for the surfactants. It can be concluded that LAP-MALDI MS can be used to analyse biological samples directly without major sample clean-up if their content of additives is not too high.