In situ reduction suitable for matrix-assisted laser desorption/ionization and liquid secondary ionization using tris(2-carboxyethyl)phosphine.

The suitability of the hydrochloride salt of tris(2-carboxyethyl)phosphine (TCEP) for in situ reduction with matrix-assisted laser desorption/ionization (MALDI) and liquid secondary ionization (LSI) mass spectrometry is evaluated. TCEP can be used to irreversibly reduce organic disulfides to thiols in water and is active at an acidic pH. We found that TCEP was suitable for partial reduction of bovine insulin deposited on the target and mixed with either sinapinic acid in MALDI or glycerol and m-nitrobenzyl alcohol in LSIMS. When TCEP was added to insulin deposited on the target without prior mixing of sinapinic acid the in situ MALDI protocol resulted in almost complete reduction.