A three section linear or two-dimensional (2D) quadrupole ion trap as a high performance mass spectrometer is described. Mass analysis is performed by ejecting ions radically out slots formed in at least two of the rods using the mass selective instability mode of operation. The slot geometry is optimized to enable ions of different mass ranges to be scanned out of differently dimensioned slots. Multiple detectors arranged to receive ejected ions in multiple directions provide the ability to simultaneously or sequentially scan or perform mass analysis of ions of different natures.