A method and apparatus for operating a mass spectrometer include providing at least two different ion sources, and coupling ion streams simultaneously from the at least two different ion sources to the spectrometer. Another method of operating a spectrometer includes a first coupling an ion stream from a first one of the ion sources into the spectrometer, next coupling an ion stream from a second one of the ion sources into the spectrometer, next coupling an ion stream from the second one of the ion sources into the spectrometer, and next coupling an ion stream from the first one of the ion sources into the spectrometer.