A W-Geometry Ortho-TOF MS with High Resolution and Up to 100% Duty Cycle for MS/MS

Abstract

Orthogonal injection time-of-flight (orthoTOF) mass spectrometry (MS) is the most prevalent form of TOFMS, owing to its greater control over incoming ion energy, the ability to correct for aberrations in incoming ion velocity and position, and its ability to provide an entire mass spectrum within a single scan. However, the duty cycle of orthoTOFMS is low compared with scanning analyzers, which can have 100% duty cycle when measuring a single type of ion. Typical duty cycles for orthoTOFMS range from 1% to 30%, depending on instrument geometry. Generally, as instrument resolution increases, duty cycle decreases. Additionally, the greatest duty cycle is achieved for the highest m/z ion recorded in the spectrum, and decreases for all other ions as a function of m/z. In a prior publication [Loboda, A.V.; Chernushevich, I.V. J. Am. Soc. Mass Spectrom. 20, 1342-1348 (20)], a novel trapping/release method for restoring the duty cycle of a V-geometry orthoTOFMS to near 100% (referred to as "Zeno pulsing") was presented. Here, we apply that method to a W-TOF geometry analyzer with analog detection. Across a m/z range of 100-2000, sensitivity gains of ~5-20 are observed, for total ion currents approaching ~10⁷ ions·s^-1. Zeno pulsing, or similar strategies for restoring duty cycle, will continue to be important as instrument resolution in orthoTOFMS is increased through the use of ion mirrors. Graphical Abstract ᅟ.

Keywords: Collision cell; Duty cycle; Ion trapping; Mass resolution; Quadrupole; Time-of-flight mass spectrometry; Zeno; orthoTOF.