using a combination of rf and dc electric fields differences in separation of atmospheric pressure ions are significant although the techniques are not orthogonal in the strict sense they are such that the fusion of ion mobility spectra will result in signal attributes that will enhance false alarm reduction and in some cases eliminate false alarms altogether following fig1 from upper left to upper center down to lower center and finally to lower right the sequence of events is as follows 1 u201c primary u201d ions are formed as a result of electric discharge or ionizing radiation primary ions react with neutral species target analytes to form analyte ions and these ions drift into a reaction region where they are u201c trapped u201d by a grid that is electrically biased to prevent ions from passing through 2 periodically the grid voltage is lowered for a short period typically one to two hundred microseconds which allows a packet of ions to enter the separation or drift region 3 this packet of moves through the drift region under the influence of a constant electric field e where separation occurs according to the size of the ions and the charge on the ions u2014 the smaller ions move faster than the larger ions 4 as ions impact an ion collector a current is created in external circuitry and the variation of the ion current with u201c drift time u201d is an ion.