Obtaining tandem mass spectrometry data for multiple parent ions in an ion population

A method of tandem mass spectrometry using a mass spectrometer comprising an ion source, a first trapping region, a second trapping region comprising a plurality of elongate electrodes, a collision cell, an ion detector and a time of flight mass analyzer, the method comprising:

• a filling stage comprising
• operating the ion source to generate ions,
• introducing ions generated by the ion source into the first trapping region, and
• operating the first trapping region to trap a primary set of precursor ions introduced from the ion source, the primary set of precursor ions having a relatively large range of m/z values;
• a first selection/analysis stage comprising
• operating the first trapping region to eject a first secondary subset of the primary set of precursor ions, the first secondary set of precursor ions having an intermediate range of m/z values, thereby to travel to the second trapping region while retaining other ions from the primary set of precursor ions in the first trapping region,
• operating the second trapping region to trap ions from the first secondary subset of precursor ions introduced from the first trapping region,
• operating the ion detector to obtain a mass spectrum of trapped ions from the first secondary subset of precursor ions, and
• performing a plurality of fragmentation/analysis stages of trapped ions from the first secondary subset of precursor ions;
• a second selection/analysis stage comprising
• operating the first trapping region to eject a second secondary subset of the primary set of the precursor ions, the second secondary subset of precursor ions having a different intermediate range of m/z values, thereby to travel to the second trapping region,
• operating the second trapping region to trap ions from the second secondary subset of precursor ions introduced from the first trapping region,
• operating the ion detector to obtain a mass spectrum of trapped ions from the second secondary subset of precursor ions, and
• performing a plurality of fragmentation/analysis stages of trapped ions from the second secondary subset of precursor ions;
• wherein each of the respective plurality of fragmentation/analysis stages comprises
• operating the second trapping region to eject a tertiary subset of precursor ions with a relatively narrow range of m/z values substantially orthogonally with respect to the direction of elongation of the electrodes such that they are introduced into the collision cell,
• operating the collision cell such that ions from the tertiary subset of precursor ions ejected from the second trapping region are fragmented,
• introducing fragmented ions from the collision cell into the time of flight mass analyzer, and
• operating the time of flight mass analyzer to obtain a mass spectrum of the fragmented ions,
• wherein the tertiary subsets of precursor ions for each of the secondary subsets have different relatively narrow ranges of m/z values.

A tandem mass spectrometer comprising an ion source, an ion trap, a collision cell and a time of flight analyzer, wherein:

• the ion trap comprises plurality of elongate electrodes operable to provide a trapping field to trap ions introduced from the ion source with a relatively broad range of m/z values and to eject trapped ions over a relatively narrow range of m/z values such that the ions are ejected from the ion trap substantially orthogonally to the direction of elongation of the electrodes;
• the collision cell is operable to accept ions ejected from the ion trap substantially orthogonally and to fragment accepted ions;
• and
• the time of flight mass analyzeris operable to acquire a mass spectrum of the fragmented ions.