Miniature ion mobility spectrometer cell

Abstract

A miniature ion mobility spectrometer call using resistive coated ceramic electrodes is described. Its construction, performance and results of parametric studies are reported. The cell has a total ion current in the range 1 to 8*10-10 A and a minimum baseline ion current of 1.9*10-11 A. The total ion current less baseline ion current difference affects sensitivity through scaling relationships with the reactant and product ion currents. Because a membrane inlet is used for sample introduction, the carrier and drift gas flow rates both affect sensitivity. Although protonated quasi-molecular ions of sample molecules are found to be stable in the cell, protonated dimer ions dissociate in the higher electric fields which can be applied to the cell. Resolution of ion mobility peaks scales as the two-thirds power of the drift length squared divided by the gate width applied to the shutter grid. A microprocessor-controlled environmental monitoring system has been assembled using the cell as a sensor.