A solution-phase digestion process is described. Intact proteins are digested to obtain parent peptides, which are separated and subsequently mass analyzed. Individual parent peptides are digested to obtain daughter peptides, which are also subsequently mass analyzed. Accurate mass data obtained from mass analysis of both parent and daughter peptides are correlated with separations data obtained during separation of the parent peptides to provide peptide identification. The process is expected to provide unique peptides by which to identify intact proteins in a sample without need for MS/MS gas-phase fragmentation.