Abstract: In an ion trap mass spectrometer including an ion trap space surrounded by a ring electrode and two end cap electrodes placed opposite each other with the ring electrode between them, a method of trapping object ions of a predetermined mass-to-charge ratio in the ion trap space more assuredly and effectively. The method includes the steps of: applying an RF voltage to the ring electrode to trap the object ions; and applying an auxiliary AC voltage to the end cap electrodes, where the auxiliary voltage has a frequency spectrum with a first notch at the basic frequency of the object ions and a second notch at a a beat frequency. Then the second stage is performed where another auxiliary AC voltage of the beat frequency is applied to the end cap electrodes to expel non-object ions still remaining in the ion trap space.

Abstract: In an ion trap mass spectrometer including an ion trap space surrounded by a ring electrode and two end cap electrodes placed opposite each other with the ring electrode between them, a method of trapping object ions of a predetermined mass-to-charge ratio in the ion trap space more assuredly and effectively. The method includes the steps of: applying an RF voltage to the ring electrode to trap the object ions; and applying an auxiliary AC voltage to the end cap electrodes, where the auxiliary voltage has a frequency spectrum with a first notch at the basic frequency of the object ions and a second notch at a a beat frequency. Then the second stage is performed where another auxiliary AC voltage of the beat frequency is applied to the end cap electrodes to expel non-object ions still remaining in the ion trap space.

Abstract: A small AC voltage V.sub.a .multidot.cos.omega..sub.a t (perturbation AC voltage) is applied to the electrodes of a quadrupole mass spectrometer besides the normal DC and AC voltages U and V.multidot.cos.omega.t (mass scanning voltages). The perturbation AC voltage generates unstable bands UB1, UB2 in a triangular stable region SR and cut off the skirts of the peak profile of every mass, which enhances the resolution of masses in the mass spectroscopy and improves the reliability of the measurement results.

Abstract: An inductively-coupled radio frequency plasma mass spectrometer comprises an induction coil for generating a high frequency magnetic field, a plasma torch for causing a plasma by introducing an aerosol therein, and an electrostatic shield, interposed between the induction coil and the plasma torch, for shielding off the plasma from the electric field by the induction coil.

Abstract: A quadrupole mass spectrometer wherein the quadrupole and the ion detector are not in axial alignment with each other, with an exit apertured plate having an exit aperture disposed adjacent the exit end of the quadrupole and an entrance apertured plate having an entrance aperture disposed in front of the ion detector. An electrode in the form of a hollow cylinder or a plate having a circular aperture formed therein is interposed between the exit apertured plate and the entrance apertured plate so that the central axis of the aperture of the electrode is aligned with that of the entrance aperture to the ion detector. A controller is provided to apply a voltage individually to the exit apertured plate and the interposed electrode so that the action of the fringing electric field about the exit end of the quadrupole to cause divergence of the ion beam is substantially suppressed.