Patent ID: 7880135

Claim:
A mass spectrometer capable of an MS n analysis (n≧3), comprising: a) an input section configured to allow an analyst to enter and set a mass difference or information corresponding thereto between a precursor ion in an (n−2) th ion species' selection/dissociation operation and product ions created thereby, as a selection reference for a precursor ion of an (n−1) th ion species' selection/dissociation operation; b) a valence determiner configured to determine a valence of at least one of selected precursor ions; and c) a precursor ion selector configured to search for an ion species adapted to the selection reference entered and set through the input section, when performing an MS n analysis, in consideration of a valence determined by the valence determiner as to one of previous precursor ions, from among ion species corresponding to a peak appearing in a mass spectrum obtained by an MS n-1 analysis, and then to determine the ion species as a precursor ion of an (n−1) th ion species' selection/dissociation operation in the MS n analysis.