Mass spectrometer and mass spectrometry method

A mass spectrometer comprising:

• a reaction chamber into which a precursor ion is introduced;
• a radical generation part configured to generate a radical of a known type;
• a radical supply part configured to supply the radical generated by the radical generation part to the reaction chamber into which the precursor ion is introduced to generate fragment ions and an adduction;
• an ion detector, a gain of which is set to a gain with which no halation occurs in the fragment ions and the adduction but halation occurs in the precursor ion;
• a measurement control part configured to measure ions including the precursor ion, the fragment ions, and the adduction by using the ion detector to obtain a mass spectrum;
• and
• an accurate mass estimation part configured to specify a peak corresponding to the precursor ion in the mass spectrum, specify a peak of the adduction by searching a predetermined mass range centered on a mass value obtained by adding a mass of an atom or molecule derived from the radical, assumed to be attached to the adduction, to a mass obtained from the peak corresponding to the precursor ion, and estimate an accurate mass of the precursor ion by subtracting an accurate mass of the atom or molecule derived from the radical, assumed to be attached to the adduct ion, from an accurate mass obtained from the peak of the adduction.