Patent ID: 7074570

Claim:
A method of identifying a polypeptide, which method comprises the steps of (a) derivatizating, in an aqueous solution, the N-terminus of the polypeptide, or the N-termini of one or more peptides of the polypeptide, with at least one acidic reagent containing a sulfo moiety coupled to an ester moiety to provide one or more peptide derivatives, which reagent exhibits a half-life in aqueous solution of not less than 10 minutes at room temperature, to prepare one or more derivatives; (b) analyzing at least one said derivative using a mass spectrometric technique to provide a fragmentation pattern; and (c) interpreting the fragmentation pattern obtained to identify the polypeptide; wherein said at least one acidic reagent is an N-hydroxysuccinimide ester of the compound of the formula wherein Y is a spacer which contains aliphatic and/or aromatic fragments and may optionally include additional sulfonic acids.