Multiplexed ion mobility spectrometer (IMS)- time-of-flight (TOF) instrument provides >10-fold sensitivity enhancement over that of the conventional IMS-TOF apparatus. When combined with ion accumulation prior to ion introduction into an IMS drift tube, multiplexing enables the coupling of a continuous ion source with an inherently pulsed IMS-TOF instrument. The novelty of the proposed approach is based on implementation of multiplexing with ion accumulation for two-dimensional ion separation.