Liquid chromatography–mass spectrometry and capillary electrophoresis combined approach for separation and characterization of multicomponent peptide mixtures: Application to crude products of leuprolide synthesis

A sequential combination of reversed-phase liquid chromatography–mass spectrometry (LC–MS) and capillary electrophoresis (CE) has been explored in order to perform separation and characterization of a multicomponent peptide mixture from the synthesis of leuprolide. The mixture was first analyzed and fractionated by LC–MS, and the collected fractions were subsequently separated by CE. Unambiguous identification of the electrophoretic peaks was achieved by injecting the collected fractions separately and spiking the leuprolide crude mixture. Furthermore, structural information about the components of the mixture provided by several semi-empirical migration models has been used to check the accuracy of the structures previously proposed by LC–MS. Combination of the two orthogonal techniques results in an enhancement of their individual selectivity characteristics.