Orthogonal acceleration single-pass time-of-flight mass spectrometry for determination of the exact masses of product ions formed in tandem mass spectrometry experiments

Abstract

A hybrid magnetic sector/orthogonal acceleration single-pass time-of-flight (oaTOF) mass spectrometer has been used to measure the exact masses of product ions formed in high- and low-collision-energy MSMS experiments. Methods for both external and internal calibration of the mass scale have been evaluated. Mass accuracies of ±25 ppm are routinely achieved for product ions having masses greater than 200 Da. Best case mass accuracies of ±10 ppm have been obtained. Mass accuracy at low mass is limited by the current speed of the time-to-digital converter (TDC). Experiments at reduced accelerating voltages suggest that doubling the TDC acquisition rate will increase low-mass accuracy six-fold. A number of applications of exact mass MSMS are presented, including: characterization of a side-reaction product formed in a combinatorial library synthesis, differentiation of isobaric residues in small peptides and a ‘mimicked’ MS3 measurement to confirm the identity of an unusual product ion previously observed in an ion trap MSMS experiment. © 1997 John Wiley & Sons, Ltd.