A mass spectrometer includes at least one ion selector, at least one collision cell, and an ion path switching device arranged to define a looped ion path around which ions derived from a sample may be sent multiple times (without reversal of ion travel) in order to effect a desired number of isolation/fragmentation cycles for MSn analysis. When the desired number of isolation/fragmentation cycles have been completed, the ion path switching device directs the ions to a detector or a separate mass analyzer for acquisition of a mass spectrum.