A desalting approach for MALDI-MS using on-probe hydrophobic self-assembled monolayers

One of the problems encountered in preparing samples for matrix-assisted laser desorption/ionization (MALDI) analysis is the presence of nonvolatile salts in the sample. This difficulty is often exacerbated by the necessity to prepare the sample in the appropriate sample-to-matrix ratio. This paper reports a probe surface derivatization method that greatly simplifies this sample preparation process. By constructing self-assembled monolayers of octadecyl mercaptan (C18) on the MALDI probe surface, we were able to generate a surface capable of reversibly binding polypeptides via hydrophobic interactions, which in turn, permits the analyte to be easily concentrated and desalted directly on the probe tip.