A Systematic Investigation of the Best Buffers for Use in Screening by MALDI-Mass Spectrometry.

Matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS) offers a label-free alternative for the screening of biochemical targets in both 1536- and 6144-assay formats, as well as potentially providing increased sensitivity, reproducibility, and the simultaneous detection of multiple assay components within a specified m/z range. Ion suppression effects are one of the principal limitations reported for MS analysis. Within MALDI-MS screening, it has been identified that certain biochemical components incorporated into the assay (e.g., the buffers used to preserve the physiological conditions of the enzyme, salts, and other additives) induce suppression of the analyte ion signals monitored. This poorly understood phenomenon of ion suppression is a key reason the screening community has been reluctant to shift their investigations toward MS methods with reduced sample cleanup. Using acetylcholine as an assay substrate mimic, we have generated robust data to quantify the degree to which the most highly used components (base buffers, additional components, detergents, cell culture media, and other additives) within current screening assays are compatible with MALDI-MS. Here, the most suitable buffers and components, along with their identified optimal concentrations in terms of limiting ion suppression effects, are proposed for use in screening assays measured by MALDI-MS.