Government agencies across the globe continuously evaluate security equipment, which is employed in Drugs and Explosives detection applications. Security equipment can be broadly divided into two categories: ‘bulk’ detectors such as metal detectors or X-Ray scanners, which rely on the presence of a significant amount of a material; and ‘trace’ detectors, such as ‘sniffer’ systems, which detect the presence of minute quantities of a threat material which may remain after handling illicit materials.
Trace detectors are used for explosives detection at locations such as airports, stadia or public buildings, and for drugs detection at ports of entry or in nightclubs. Whether the need be for the detection of drugs, explosives or even chemical warfare agents, the authorities must determine the efficacy of the various solutions proposed to address terrorist or criminal threats. To do this, governments must undertake tests to determine the limit of detection of the equipment proposed to a range of target analytes.
Recent work by Tam et al of the Canada Border Services Agency (CBSA) has advocated the use of the ‘Scentinel’ system to massively reduce the time required to obtain results. Government bodies like the CBSA regularly conduct hundreds of experiments to understand the performance of the expanding number of trace detectors available commercially. New iterations of existing designs, not to mention urgent requirements to study new drugs or explosives that may come to light, exacerbate the number of experiments required.
The CBSA paper concluded that the Scentinel system desorber is highly efficient for a range of explosives, and that the results it produces are quantitative (i.e. the instrument response is directly proportional to the amount of explosive present). The CBSA confirmed that the analysis undertaken by the Scentinel takes a few minutes compared to the many hours required for conventional analysis and that no sample pre-treatment is required (no solvents, no derivatisation, or filtration).
The Scentinel is designed and manufactured by Bristol based Mass Spec Analytical Ltd. The instrument is based on an ABSciex triple quadrupole tandem mass spectrometer, which has been modified to incorporate a thermal desorption sample inlet system. The device simply heats samples to evaporate the compounds of interest, and draws the vapour into the mass spectrometer for analysis. This enables target analytes, such as drugs and explosives, to be analysed within seconds without the extensive sample preparation required for analysis by Gas chromatography–mass spectrometry (GCMS), even if they are in the presence of significant amounts of dirt and grease. Compounds are separated within the mass spectrometer itself, completely eliminating the need for chromatography. Tandem mass spectrometers are essentially two mass spectrometers back to back. The first is used to separate the compounds of interest according to their molecular mass. The substance is then broken up before characteristic fragments are looked for by the second mass spectrometer. This type of analysis has been called ‘fast and dirty’, since detection is achieved very rapidly with no sample clean-up, precisely the reason why its use has gained popularity with the CBSA and other authorities tasked with evaluating trace detector technologies.
The approach of directly analysing materials by thermal desorption tandem mass spectrometry (TD-MSMS) has also been successfully applied to the forensic analysis of drugs of abuse. For many years, Mass Spec Analytical Ltd. has provided an analysis service to law enforcement agencies, both in the UK and overseas. Often, the authorities wish to know whether a particular item is contaminated with a certain substance; for example, “is this jacket contaminated with amphetamine?” They are not necessarily interested in whether other substances may also be present. This is ideally suited to the use of TD-MSMS, where target compounds (in this case amphetamine) are looked for. The conventional method of analysis would be to shake the garment over a clean surface, collect the dust, extract it using a solvent , filter the extract and finally analyse it by GCMS. Alternatively, a swatch could be cut from the garment and extracted in a similar way. Either way, the total analysis time would be in excess of an hour. By contrast, by bringing the garment into contact with a moving belt that goes directly into a TD-MSMS device, the same result can be obtained in a matter of seconds. Not only that, but TD-MSMS is inherently more sensitive than GCMS (lower amounts can be detected) and by applying different areas of the jacket to the belt (sleeves, cuffs, inside and outside of pockets, etc.) far more information can be obtained in a much shorter time than it takes to conduct a single analysis by GCMS.
To date, the TD-MSMS technique has been most widely applied to the analysis of paper money for traces of drugs. Early methods of analysis relying on GCMS have now been almost entirely superseded by the use of TD-MSMS.
Chromatography free analytical solutions, coupled with the use of tandem mass spectrometry, are increasingly gaining acceptance in the field of analytical chemistry. The CBSA requirement for testing explosives detectors is just one such application; many more await discovery.