Introduction Insulin is perhaps one of the best known and earliest peptide therapeutics.Quantification of biologics,such as insulins,has historically been performed using ligand binding assays(LBAs)such as ELISAS.LC/MS/MS,however,has certain advantages over LBAs,such as shorter development times,higher accuracy and precision,the ability to multiplex,no cross-reactivity,and the ability to readily distinguish between closely related insulins.