Patent ID: 7566870

Claim:
A mass spectrometer comprising: a linear ion trap to implement accumulation, isolation, dissociation, and ejection periods for the ion generated in an ion source; a detector to detect the ion ejected from said ion trap; a power supply to apply at lease one of RF voltage, supplemental AC voltage, and DC voltage to said ion trap; and a controller to control voltage values of said power supply and said ion trap, wherein said controller sets the ion trap, the power supply and the detector to sequentially execute ion accumulation and ejection periods during a first mass spectrometry analysis (“MS1 analysis”), and then to sequentially execute ion accumulation, isolation, dissociation, and ejection periods during a second mass spectrometry analysis (“MS2 analysis”) subsequent to the first mass spectrometry analysis, in the ion accumulation period of the MS1 analysis, ions are accumulated near an center axis of the ion trap, and then ions lighter than a first low mass cut off (LMCO) are ejected out of the ion trap to leave only precursor ions therein, in the ion ejection period of the MS1 analysis, said precursor ions are ejected out of the ion trap into a collisional damping chamber to subject to a first mass spectrometry in the chamber, in the ion accumulation period of the MS2 analysis, ions accumulated and saturated in the ion trap are subject to a supplemental AC voltage to resonant-oscillate the ions and to eject ions outside of a target mass range out of the ion trap, in the ion isolation period of the MS2 analysis, ions remaining in the ion trap are accumulated near the center axis of the ion trap, ions remaining in the ion trap and lighter than a second LMCO are ejected out of the ion trap, the second LMCO being higher than the first LMCO, in the ion dissociation period of the MS2 analysis, ions remaining in the ion trap are applied with another supplemental AC voltage to dissociate the ions into fragmented ions, in the ion ejection period of the MS2 analysis, said fragmented ions are ejected out of the ion trap into the collisional damping chamber to subject to a second mass spectrometry in the chamber, said controller sets said voltage value for at least one of said periods of said ion trap in the second mass spectrometry, on the basis of an ion amount in or just before said at least one period of said ion trap as calculated based on a measurement result of the first mass spectrometry.