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: 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: 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 an inlet for an analyte substance opening into an ionization region that produces ions of the substance. Parallel grid electrodes extend laterally across the ion flow path and apply an electric field to the ions that is switchable between a relatively low magnitude alternating field that varies in magnitude over multiple periods and an asymmetric alternating field of sufficiently high magnitude to cause differential mobility effects. A collector collects the passed ions, and an indication of the nature of the analyte substance is produced from the collected ions passed during both the low and high field intervals. Also disclosed is the application of a substantially alternating field between the electrodes, which field varies between a low value and a higher value over a time exceeding that of the alternating period.

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 detection system comprises a housing having a sample inlet and a gas outlet, and a preconcentrator. The preconcentrator can include a microelectromechanical system (MEMS) configured to accumulate or release a dopant at selected times, and can be located inside or outside the housing. The detection system can include an ion mobility spectrometer, a mass spectrometer, or a combination thereof. A method of analyzing a substance comprises supplying a sample gas or vapor comprising the substance, accumulating a dopant in a first preconcentrator, releasing the dopant at selected times from the preconcentrator to an area containing the sample, ionizing the substance to generate detectable species, separating the detectable species, and determining the detectable species by a detection unit. The system and method allow the rapid introduction and removal of dopant to facilitate fast and accurate identification of the sample.

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 an inlet for an analyte substance opening into an ionization region that produces ions of the substance. Parallel grid electrodes extend laterally across the ion flow path and apply an electric field to the ions that is switchable between a relatively low magnitude alternating field that varies in magnitude over multiple periods and an asymmetric alternating field of sufficiently high magnitude to cause differential mobility effects. A collector collects the passed ions, and an indication of the nature of the analyte substance is produced from the collected ions passed during both the low and high field intervals. Also disclosed is the application of a substantially alternating field between the electrodes, which field varies between a low value and a higher value over a time exceeding that of the alternating period.

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: 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 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 system comprising: an ion mobility detector; a gas/vapor circulating system for the ion mobility detector into which samples of gases and vapors of interest may be drawn for detection by the ion mobility spectrometer; the circulating system comprising an ion mobility cell, means for drying and/or cleaning the circulating gases/vapors in the circulating system, a dopant source, and means for causing circulation of the gases/vapors within the circulating system; in which the dopant source and the means for drying and/or cleaning the circulating gases/vapors are combined, whereby the need for a physically separate dopant source for the system is obviated. The dopant source material may be combined with the material for drying and or cleaning the circulating gases/vapors.

Abstract: An ion mobility spectrometer system comprising: an ion mobility detector; a gas/vapor circulating system for the ion mobility detector into which samples of gases and vapors of interest may be drawn for detection by the ion mobility spectrometer; the circulating system comprising an ion mobility cell, means for drying and/or cleaning the circulating gases/vapors in the circulating system, a dopant source, and means for causing circulation of the gases/vapors within the circulating system; in which the dopant source and the means for drying and/or cleaning the circulating gases/vapors are combined, whereby the need for a physically separate dopant source for the system is obviated. The dopant source material may be combined with the material for drying and or cleaning the circulating gases/vapors.

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.

Abstract: A corona discharge ionization source, for use for example with an ion mobility spectrometer, comprises an adjustable corona point electrode (20) which is held transversely within a cylindrical target electrode (14). A corona discharge is produced by a constant or pulsed potential difference between the two electrodes. In alternative embodiments, there may be a further corona discharge electrode (58), providing additional control, and also an annular counterelectrode (60) surrounding the further point electrode (58).