Abstract: A field asymmetric ion mobility spectrometer (FAIMS) has an analyte ion source assembly by which an analyte substance is ionized and supplied to the inlet of the spectrometer. The ion source assembly has an upstream source of clean, dry air and two ion sources of opposite polarity arranged at the same distance along the flow path. The ion sources are arranged so that the overall charge of the plasma produced is substantially neutral. The analyte substance is admitted via an inlet downstream of the ion sources and flows into a reaction region of enlarged cross section to slow the flow and increase the time for which the analyte molecules are exposed to the plasma.

Abstract: An ion mobility spectrometer has two drift chambers and a common, doped reaction region. Each drift chamber includes an ion modifier, such as one that fragments the doped ions by a high electrical field. One of the drift chambers is doped and the other is undoped. In this way, the dopant adducts are removed by the modification process but then recombine with dopant only in the doped chamber so that different outputs are produced by the two drift chambers.

Abstract: An ion mobility spectrometer has a pair of electrodes and midway along the drift chamber. A high field is applied between the electrodes and sufficient to modify ions in the region of thee electrodes such that they move at a different rate towards the collector plate. This is used to modify the time of flight of selected ions or ion clusters and enable identification of ambiguous peaks on the IMS spectrum.

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 has two drift chambers and a common, doped reaction region. Each drift chamber includes an ion modifier, such as one that fragments the doped ions by a high electrical field. One of the drift chambers is doped and the other is undoped. In this way, the dopant adducts are removed by the modification process but then recombine with dopant only in the doped chamber so that different outputs are produced by the two drift chambers.

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 has a pair of electrodes (13A) and (13B) midway along the drift chamber (7). A high field is applied between the electrodes (13A) and (13B) sufficient to modify (e.g. fragment) ions in the region of the electrodes such that they move at a different rate towards the collector plate (8) . This is used to modify the time of flight of selected ions or ion clusters and enable identification of ambiguous peaks on the IMS spectrum.

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.

Abstract: A field asymmetric ion mobility spectrometer (FAIMS) has an analyte ion source assembly by which an analyte substance is ionized and supplied to the inlet of the spectrometer. The ion source assembly has an upstream source of clean, dry air and two ion sources of opposite polarity arranged at the same distance along the flow path. The ion sources are arranged so that the overall charge of the plasma produced is substantially neutral. The analyte substance is admitted via an inlet downstream of the ion sources and flows into a reaction region of enlarged cross section to slow the flow and increase the time for which the analyte molecules are exposed to the plasma.

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 has two drift chambers and a common, doped reaction region. Each drift chamber includes an ion modifier, such as one that fragments the doped ions by a high electrical field. One of the drift chambers is doped and the other is undoped. In this way, the dopant adducts are removed by the modification process but then recombine with dopant only in the doped chamber so that different outputs are produced by the two drift chambers.

Abstract: An ion mobility spectrometer has an inlet opening into an ionization region including a conventional ionization source. A series of several charged, circular electrode plates with aligned apertures extending therethrough provides a drift region on the opposite side of the ionization region from the inlet. A gas inlet connected to a source of clean, dry flushing gas opens between the ends of the drift region, with the gas flowing against the ion flow to one side to remove water molecules from the analyte. Gas flowing in the opposite direction is effective to help drive the dry analyte ions to an analysis region provided by two parallel asymmetric field plates.

Abstract: IMS apparatus has a preconcentrator (20) connected at the inlet (2) of an IMS detector (1) such that all gas supplied to the detector flows through the preconcentrator. The preconcentrator comprises a metal tube (21) having a layer of silicone rubber (24) exposed on its inner surface (25). An electrical resistance heating element (22) extends under the silicone rubber layer (24) and is connected to a power source (23) such that the silicone rubber layer can be periodically heated to desorb substances absorbed by the layer and release them to flow to the IMS detector 1 at a higher concentration. The silicone rubber (24) can operate in the desorption phase in the presence of air without degradation.

Abstract: An ion mobility spectrometer has a pair of electrodes (13A) and (13B) midway along the drift chamber (7). A high field is applied between the electrodes (13A) and (13B) sufficient to modify (e.g. fragment) ions in the region of the electrodes such that they move at a different rate towards the collector plate (8) . This is used to modify the time of flight of selected ions or ion clusters and enable identification of ambiguous peaks on the IMS spectrum.

Abstract: An IMS or other analytical instrument has a corona discharge needle (20) to ionize sample gases or vapours. A gate (3) is opened or closed to admit or prevent entry of the ions produced by the corona discharge to a drift chamber (4). The operation of the corona discharge needle (20) and the gate (3) are controlled such that the gate is open during at least two discharges, to admit faster ions produced by the most recent discharge together with slower ions produced by an earlier discharge.

Abstract: An ion mobility spectrometer comprises an ion mobility cell (10) into which molecules of a sample to be analysed are introduced. The ion mobility cell (10) is doped with ions produced by a corona discharge ionisation source (40). In one mode of operation, the corona discharge ionisation source (40) operates to produce a continual dopant stream, and in a second mode of operation, the corona discharge ionisation source (40) produces dopant ions selectively. In the non-continuous mode of operation, the ion mobility cell (10) may be doped with chemical dopant ions instead, switching between the two dopant regimes being accomplished very rapidly. The ion mobility spectrometer is particularly suitable for the detection of explosive compounds and narcotics, the ion mobility spectrum of explosives doped with ions from the corona discharge ionisation source differing from the ion mobility spectrum of such explosive compounds doped with chemical dopants.