peptide purity FAQ

Multiple peaks mean impurities, but the question is what kind. If the secondary peaks appear at retention times very close to the primary peak (within 1–2 minutes), they're likely structurally related. Deletion sequences (n−1 or n−2 peptides missing one or two amino acids), diastereomers (wrong stereochemistry at one position), or incomplete side-chain deprotection. These impurities can interfere with biological assays because they may bind the same receptor or enzyme with different affinity. If the secondary peaks are distant (>5 minutes difference), they're probably unrelated contaminants from synthesis reagents or column bleed. Request the supplier identify all peaks >2%. Legitimate suppliers can tell you exactly what they are.