Quadrupole mass filter acceptance in stability island created by double-frequency quadrupole excitation.

Increase in quadrupole mass filter resolution at separation in narrow band stability island (X-band) formed by biharmonic resonance excitation of ion oscillation is discussed. X-band and the normal working quadrupole mass filter modes are compared at theoretical resolution of 10,000 and different separation times. Transmission curves, acceptance ellipses parameters, and acceptance characteristics are obtained by numerical simulation. Transmission coefficients are approximately the same in both modes. Dependence of acceptance ellipses parameters on ion inlet phases has a complicated oscillating form in the X-band mode. Acceptance contours calculated for given transition levels have been compared. At low acceptance level, the combined acceptance in the X-band mode was found to be one order of magnitude higher than in the normal mode.