| abstract |
Exemplary methods include preparing peptides free of disulfide bonds, scrambled disulfide-bonded peptide standards, and native disulfide-bonded peptide standards according to the sequence of the protein drug product region comprising disulfide bonds, digesting a sample of protein drug product into peptides isolating the protein drug product peptide, analyzing the peptide standard and the protein drug product peptide, comparing retention times to identify scrambled and native disulfide binding peptides, and scrambled disulfide binding peptides quantifying the level of |