We have found focusing/operating conditions that allow use of a commercial quadrupole mass filter for producing ion beams that simultaneously have high mass and kinetic energy resolution, and good transmission efficiency. Under proper conditions, our design perturbs the ion beam energy distribution by only ∼50 meV, while allowing mass resolution (M/ΔM)≥100, and net transmission of ∼50%. The critical factors are injection/collection lens design, an exit aperture which rejects ions that have been strongly perturbed, and stable dc balance in the quadrupole electronics.