Tandem mass spectrometry data processing system

A tandem mass spectrometry data processing system for processing MSn spectrum data obtained by performing a mass spectrometry for product ions obtained by dissociating ions collectively selected as precursor ions, the precursor ions originating from a plurality of different compounds and having mass-to-charge ratios within a predetermined mass-to-charge-ratio width, the system comprising at least one processor to implement:

• a) a product ion assignment determiner
• for obtaining mass-to-charge-ratio values of a plurality of ions selected as the precursor ions from MSn-1 spectrum data obtained by an actual measurement, where a difference of the mass-to-charge ratio values is less than 0.5 Da, and
• for determining, for each product ion, which precursor ion among the plurality of precursor ions is an origin of the product ion, by verifying consistency between a composition formula estimated from a mass-to-charge ratio of the product ion and each of composition formulae estimated from the mass-to-charge ratios of the precursor ions, or by determining a similarity between a mass defect which is a portion after a decimal point of a mass-to-charge-ratio value in atomic mass unit (Da) of the product ion and a mass defect which is a portion after a decimal point of a mass-to-charge-ratio value in Da of each precursor ion;
• and
• b) a data separator for reconstructing MS″ spectrum data of product ions for each of the precursor ions, based on a result of a determination by the product ion assignment determiner.