Utilization of Immonium Product Ions for the Determination of Peptides with Intra-loops in Biological Matrices

Abstract

Triple quadrupole mass spectrometers are generally not considered a choice of instrument for determination of peptide molecules, for the reason that a collision cascade or a multiple fragmentation in the triple quadrupoles tends to decrease the sensitivity of peptide detection. Vasopressin, a peptide drug with an intra-chain disulfide bond, however, was found to generate a different fragmentation pattern. Its 20 member intra-loop went through an abrupt bond cleavage and structurally distinctive immonium ions produced in the secondary fragmentation were observed in abundance. With these immonium ions, an effective methodology for analyzing the peptides with intra-loops in biological matrices was developed in this report.