A simple and effective method for detecting precipitated proteins in MALDI-TOF MS.

MALDI−TOF MS has developed rapidly into an essential analytical tool for the life sciences. Cinnamic acid derivatives are generally employed in routine molecular weight determinations of intact proteins using MALDI−TOF MS. However, a protein of interest may precipitate when mixed with matrix solution, perhaps preventing MS detection. We herein provide a simple approach to enable the MS detection of such precipitated protein species by means of a “direct deposition method” -- loading the precipitant directly onto the sample plate. It is thus expected to improve routine MS analysis of intact proteins.