Patent ID: 8258467

Claim:
A mass-analyzing method using a multi-turn time-of-flight mass spectrometer for making a variety of ions departing from an ion source fly along a loop orbit repeatedly plural times and then for introducing the ions into a detector to obtain a mass spectrum based on a detection signal, in which a conversion formula between a flight time and a mass-to-charge ratio is memorized, the conversion formula being obtained based on a result of an actual measurement of a flight time of an ion whose mass-to-charge ratio is previously known, the mass-analyzing method comprising the steps of: a) a first measurement mode performing step for obtaining an overtakingless time-of-flight spectrum based on a detection signal obtained by a detector by performing a mass analysis of a sample to be measured in a first measurement mode in which ions are made to fly without multi-turning along the loop orbit or to multi-turn along the loop orbit until they undergo a specific number of turns which ensures that a catching or overtaking of different kinds of ions will not occur; b) a second measurement mode performing step for performing a plurality of mass analyses of the sample to be measured while changing a timing of deviating ions from the loop orbit in such a manner that ions of a same kind undergo a different number of turns, each of the mass analyses being performed in a second measurement mode in which ions are deviated from the loop orbit and introduced into the detector at or after a predetermined point in time after they are made to multi-turn so that an overtaking of the ions will occur on the loop orbit, and for obtaining different overtaking time-of-flight spectra based on a detection signal provided from the detector; and c) a computation processing step for obtaining mass spectra respectively corresponding to the plurality of overtaking time-of-flight spectra by performing an intensity distribution processing in which: an assumed flight time without an overtaking is computed for each of peaks on each of the overtaking time-of-flight spectra obtained by performing the second measurement mode by using a plurality of assumed numbers of turns and the conversion formula; peaks respectively corresponding to the plurality of assumed flight times are identified on the overtakingless time-of-flight spectrum to obtain intensity information on the peaks; and intensities of original peaks on the overtaking time-of-flight spectrum are distributed, in accordance with the intensity information, to mass-to-charge ratios corresponding to the assumed flight times.