Unbalanced Driving Voltages in a Quadrupole Mass Filter

RATIONALE: In the development of quadrupole mass spectrometers, there is a growing interest in understanding the modified first stability region under conditions of unbalanced DC and RF voltages. METHODS: Based on the properties of the solution to the Dirichlet problem for the Laplace equation, the potentials on the orthogonal rod pairs of a quadrupole mass filter were determined. The trajectory method was employed to calculate the stability regions and transmission contours. RESULTS: The equations of ion motion were derived in the presence of DC and RF voltage amplitude imbalances. First stability region diagrams were constructed for conditions involving asymmetry in RF and DC voltage amplitudes, as well as RF phase shifts.