Precursor accumulation in a single charge state in mass spectrometry

Abstract

An ion source ionizes a compound, producing precursor ions with different m/z values. A reagent source supplies charge reducing reagent. An ion guide is positioned between a mass filter and both the ion source and the reagent source. The ion guide applies an AC voltage and DC voltage to its electrodes that creates a pseudopotential to trap the precursor ions in the ion guide below a threshold m/z. This AC voltage, in turn, causes the trapped precursor ions to be charge reduced by the reagent so that m/z values of the trapped precursor ions increase to a single m/z value above the threshold m/z. The ion guide applies the DC voltage to its electrodes relative to a DC voltage applied to electrodes of the mass filter that causes the precursor ions with m/z values increased to the single m/z value to be continuously transmitted to the mass filter.