Systems and methods for multiplexed precursor ion selection are provided. A mass isolator includes a selection region of rods, a transmission region of rods, and a barrier electrode lens separating the selection and transmission regions. Two or more different precursor ions are selected by applying two or more different AC voltage frequencies to rods of a selection region in order to resonate the two or more different precursor ions from a continuous beam of ions. The two or more different precursor ions are transmitted by applying a DC voltage to the barrier electrode lens, creating an electric field potential barrier over which only the resonating ions are transmitted. Precursor ions of product ions from combined product ion spectra produced by multiplexed precursor ion selection are identified by grouping the target precursor ions.