Differential Mobility Spectrometer (DMS) is an ion filter, which operates in atmospheric pressure and separates ions based on their characteristic electric field behavior. The ions are created with ion reactions initiated with an ionization source. In the IonVision DMS, ions are produced with 4.9 keV photoionization.
IonVision measurement results are shown as heatmap spectra. The dispersion plot presents the ions that have passed the filter with specific parameters of the electric fields. Positive and negative ions are shown separately and different substances are visible as characteristic peaks.
In the filter, the ionized gas is exposed to an asymmetric waveform. Ideal waveform has two components: high field and low field. When the ions are under the low field, their mobility is a linear function of the field strength. When the ions are exposed to the high field, mobility has a field dependent component and thus it is a nonlinear function of the electric field. When the ions are in the filter, the field forces them to move. Oscillating ions drift towards the walls of the filter if the mobility difference is not compensated. When a small DC-field is superimposed to the oscillating field, the drifting can be cancelled and the ions can pass the filter, enabling selective ion measurement.
The IonVision maximizes the ions separation with a special waveform generator which creates ideal square shaped pulses for the DMS filter. Both positive and negative ions are measured simultaneously which maximizes the measurement speed. The speed can be further improved by concentrating the measurements on specific areas of the spectra.