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Abstract

A quadrupole mass filter (50) has a main-rod section (500) including rod electrodes arranged around a central axis C and a first pre-rod section (501) including pre-rod electrodes. Along with an RF voltage having a frequency corresponding to the m/z of an ion, DC voltage is applied to the pre-rod electrodes. The DC voltage and the amplitude of the RF voltage are determined so that a-value and q-value substantially satisfy the conditions that a≠0, (π−βx·π)N={(½)+m}π and βy·π·N={(½)+n}π, where m, n and N are natural numbers, with the X-axis direction connecting the centers of two rod electrodes facing each other across the central axis in a plane perpendicular to the central axis, the Y-axis direction connecting the centers of the other two rod electrodes in the plane, and βx and βy representing β values (0<β<1) related to a secular oscillation of an ion in the X and Y directions, respectively.

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First Claim