As an ion gate for the formation of a short ion pulse in an ion mobility spectrometer, a gridless design with two coaxial diaphragms is proposed. It has been experimentally shown that, depending on the geometric and electrical parameters of this shutter, there is an optimal duration of the electric pulse opening the gate, which provide the maximum amplitude of the ion pulse.
The paper presents an analytical model describing the dynamics of ion cloud, taking into account the action of space charge during a motion in ion mobility spectrometer — starting from the reaction region, where the shutter forms an ion pulse, and the further drift of the formed ion pulse towards the collector. The presented model lets to estimate the degree of influence of the space charge on possible ion losses and the resolution of ion mobility spectrometer. The effect of the space charge becomes noticeable, starting with the ion density of 106 cm–3. Comparison of the results obtained using the analytical model with the results of numerical solution of the initial equations shows that they practically coincide.
CHARACTERISTICS OF A GRIDLESS TWO-DIAPHRAGM ION GATE AT ATMOSPHERIC PRESSURE
