The use of segmented rods in a quadrupole mass filter as described by Brubaker, [W. M. Brubaker, Advan. Mass Spectrometry 4, 293 (1967)] permits one to reduce the energy of injected ions while still maintaining high transmission. The result, as reported by Brubaker, is that higher resolution can be obtained because low energy ions spend a longer time in the resolving field. We have also found that the use of low energy ions permits covering a wide mass range in a single scan. We have designed a circuit that changes the ac/dc ratio to maintain unit resolving power. The dimensional accuracy of the mass filter is of paramount importance for high resolving power and good transmission. It was found that virtually all relevant parameters, parallelism of rods, angle between x and y axes, angle between ion source and filter, and radius r 0 are critical for high performance.