A Method to Determine Turn Numbers in Multi-Turn TOF MS

Abstract

Although various multi-turn geometries of time-of-flight mass spectrometry (TOF MS) have been devised recently, they still suffer from a practical problem in analysis for a wide mass range. The relationship between flight time and mass to charge ratio (m/z) is not as simple as the conventional TOF MS. Because the flight length may change with m/z, turn numbers of ions must be figured out for each peak in a multi-turn TOF spectrum. This article describes a method to determine turn numbers of ions in multi-turn TOF MS. The key idea is a combination of multi-turn and reflector TOF geometries. Because a change in the reflector conditions can introduce m/z-dependent perturbation into the flight times, it is possible to estimate approximate m/z values from degrees of the perturbation. This rough estimation helps to determine the numbers of turns corresponding to m/z values. Finally the precise m/z values are derived from the numbers of turns and flight times.