Effects of tryptic peptide esterification in MALDI mass spectrometry

The effect of esterification on MALDI ion yield is investigated by using alcohols having different aliphatic chain lengths. For peptides whose ionization yields increase with derivatization, more hydrophobic alcohols tend to yield greater peak enhancements. The completeness of the reaction increases from propanol to methanol. Undesired solvolysis of the amide group in the side chain of Asn or Gin leads to unexpected ester products. Ethanol is suggested as the optimal alcohol for esterification in proteomics experiments since it yields almost complete esterification without substantial solvolysis. Ethanol esterification was employed to facilitate the identification of gel-separated proteins.