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 IMS system or the like has dopant contained in a way such that it is only released when needed. The dopant could be contained in a device (50) similar to an ink-jet printer and released as droplets (55) when required. Alternatively, the dopant could be trapped in material (156) of a molecular sieve (150) in such a way that it is not normally released into air flowing through the sieve but can be released by energising a heater (157) in the sieve.

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 ion mobility spectrometer has a drift chamber (1) with an inlet (2) at one end by which a gas or vapor being analyzed is supplied to the chamber. After ionization, molecules are admitted through a gate 8 and flow along a drift region (9) to a collector plate (11). A drift gas is flowed through the drift region against the flow of ionized molecules and is circulated along a flow path (31, 32, 40) and (30), which includes a chamber (50) including a dopant. The dopant is 2,4-pentanedione, which has been found to enhance the detection of a number of compounds especially toxic industrial chemicals and nitrogen compounds, such as those present in the breath of mammals.

Abstract: Detection apparatus including an IMS detector (1, 100) or the like has a gas inlet (10) with a gas flow path arrangement (40, 41, 102) by which sample gas is supplied to the detector. In one arrangement two regions (40 and 41) of a gas flow path arrangement are connected in parallel. The regions are provided by respective GC capillary tubing coils (40) and (41) coated internally with materials of different absorption characteristics so that the time taken for the chemical of interest to reach the detector (1) is different along the two coils, thereby giving responses in the detector at different times. Alternatively, two regions of a gas flow path could be provided by regions (104 and 106) arranged serially one after the other.

Abstract: An IMS system or the like has dopant contained in a way such that it is only released when needed. The dopant could be contained in a device (50) similar to an ink-jet printer and released as droplets (55) when required. Alternatively, the dopant could be trapped in material (156) of a molecular sieve (150) in such a way that it is not normally released into air flowing through the sieve but can be released by energising a heater (157) in the sieve.

Abstract: A portal (1) has a millimetric wave imager (10, 11) arranged to detect articles concealed on the person. A pump (21) supplies jets of air through gas outlets (20) in the lower part of the portal (1), which are directed onto the feet of the person being screened. A second pump (25) pumps air with substances released by the jets via inlets (22) to an ion mobility spectrometer (24) arranged to detect the presence of explosives or narcotics. A screen (12) indicates the presence of any suspect article or substance on the person being screened.

Abstract: An ion mobility spectrometer system includes two cells (1) and (2) driven by a drive unit (12) so that the cells operate at opposite polarities and are switched between different polarities either at regular intervals or in response to detection of a substance in one cell. Two reagents are supplied to both cells (1) and (2), one promoting detection of a substance in the positive mode and the other promoting detection of a substance in the negative mode so that there is no need to switch reagents when the polarity changes.