Linear mass calibration in the quadrupole ion‐trap mass spectrometer

A new method of operation of the quadrupole ion‐trap mass spectrometer in the resonance ejection mode is introduced, that enables one to obtain accurate, linear mass calibration. The method employs linear modulation of the excitation voltage applied to the end‐caps while scanning the RF trapping field on the ring electrode. Calibration lines can be defined by a single calibration point because they converge near the reference point where the mass and trapping voltage are equal to zero. Mass assignment accuracy is achieved which is within, or of the order of, errors usually associated with the space‐charge effect. The method was implemented on a modified ion‐trap detector for ions formed by matrix‐assisted laser desorption, but can be used with other ionization techniques and applied to both external and internal calibration routines.