A swept-field aspiration condenser as an ion-mobility spectrometer

A method is presented for using a small, low-cost, extremely simple device as an ion-mobility spectrometer. The device is a planar first-order differential aspiration condenser as described by Puumalainen, but in this case the electric field is not kept constant but is swept in discrete nonuniform steps. The result is a characteristic I(V) curve that is a function of the ion-mobility density function of the gas sample flowing through the condenser. A discrete transform is introduced, based on the equations of Tammet describing the operation of aspiration condensers, that converts the I(V) curve into the ion-mobility density spectrum and vice versa. Both the device and the method are described in theoretical detail. The method is illustrated with computer simulations and experimental data using both a prototype aspiration condenser and a conventional drift tube ion-mobility spectrometer. The results suggest this method is an attractive alternative for ion-mobility gas analysis applications.