Abstract: A method/apparatus for multiplexing plural ion beams to a mass spectrometer. At least two ion sources are provided with means of transporting the ions from the ion sources to separate two-dimensional ion traps. Each ion trap is used for storage and transmission of the ions and operates between the ion sources and the mass analyzer. Each ion trap has a set of equally spaced, parallel multipole rods, as well as entrance and exit sections into which and from which ions enter and exit the trap, respectively. For each ion trap, the entrance section is placed in a region where background gas pressure is at viscous flow. The pressure at the exit section drops to molecular flow pressure regimes without a break in the structure of the ion trap. Each trap alternately stores and transmits ions by way of a fast voltage switch applied to the ion trap exit lens.