Abstract: An ion mobility and mass spectrometer instrument includes an ion source region coupled to an ion mobility spectrometer having an ion outlet coupled to a quadrupole mass filter. An output of the filter is coupled to a collision cell which has an ion outlet coupled to an ion acceleration region of a mass spectrometer such as a time of flight mass spectrometer. The instrument is particularly well suited for sequencing analysis wherein a sample is ionized and a resulting three-dimensional ion spectrum (ion intensity vs. ion mobility and ion mass) is observed. If the spectrum reveals that no ions overlap in mobility values, the collision cell is filled with a suitable buffer gas and the instrument is reactivated whereby a complete three-dimensional spectrum of parent and daughter ions results.