Abstract: An ion mobility spectrometer or other ion apparatus has two or three grid electrodes 51 and 52; 151 to 153; 106 and 107; 106? and 107? extending laterally of the ion flowpath. An asymmetric waveform with a dc compensating voltage is applied between the electrodes to produce a field parallel to the ion flow path that affects ions differently according to their field-dependent mobility. This filters or delays different ions selectively in their passage to an ion detector 11, 111, 111? to facilitate discrimination between ions that would otherwise produce a similar output.

Abstract: An ion mobility spectrometer or other ion apparatus has two or three grid electrodes 51 and 52; 151 to 153; 106 and 107; 106? and 107? extending laterally of the ion flowpath. An asymmetric waveform with a dc compensating voltage is applied between the electrodes to produce a field parallel to the ion flow path that affects ions differently according to their field-dependent mobility. This filters or delays different ions selectively in their passage to an ion detector 11, 111, 111? to facilitate discrimination between ions that would otherwise produce a similar output.

Abstract: A FAIMS ion mobility spectrometer is arranged so that the analyte is subject to different ion chemistries at different locations along the spectrometer. Different dopants, or different concentrations of dopants or water vapor are admitted at various locations, such as at the inlet, between the inlet and the ionizer between the ionizer and the gate, between the gate and the FAIMS parallel plates, through an opening in one of the plates, or between the end of the plates and the detector.