ORTHOGONAL ACCELERATION SINGLE-PASS TIME-OF-FLIGHT MASS-SPECTROMETRY FOR DETERMINATION OF THE EXACT MASSES OF PRODUCT IONS FORMED IN TANDEMMASS-SPECTROMETRY EXPERIMENTS

A hybrid magnetic sector/orthogonal acceleration single-pass time-of-f light (oaTOF) mass spectrometer has been used to measure the exact mas ses of product ions formed in high-and low-collision-energy MSMS exper iments. Methods for both external and internal calibration of the mass scale have been evaluated, Mass accuracies of +/- 25 ppm are routinel y achieved for product ions having masses greater than 200 Da, Best ca se mass accuracies of +/- 10 ppm have been obtained. Mass accuracy at low mass is limited by the current speed of the time-to-digital conver ter (TDC), Experiments at reduced accelerating voltages suggest that d oubling the TDC acquisition rate will increase low-mass accuracy six-f old. A number of applications of exact mass MSMS are presented, includ ing: characterization of a side-reaction product formed in a combinato rial library synthesis, differentiation of isobaric residues in small peptides and a 'mimicked' MS3 measurement to confirm the identity of a n unusual product ion previously observed in an ion trap MSMS experime nt. (C) 1997 by John Whey & Sons, Ltd.