Deamidation determination using direct infusion mass spectrometry

A method for analyzing a polypeptide having one or more amino acid residues comprising an unmodified amide functional group or a deamidated amide functional group, the method comprising the steps of:

• a) injecting the polypeptide into an ion source of a mass spectrometer device;
• b) generating one or more precursor ions from the polypeptide injected into the ion source of the mass spectrometer device;
• c) performing one or more MS scans on the one or more precursor ions generated from the polypeptide and obtaining mass spectrometry data on the polypeptide, wherein obtaining mass spectrometry data comprises measuring a mass-to-charge ratio of the one or more precursor ions and/or one or more fragment ions thereof;
• d) characterizing the presence and/or amount of deamidated amide functional groups in the polypeptide based on the mass spectrometry data.