Geoff Harper reports on the burgeoning applications of MS and GC in narcotics and explosives detection
The use of mass spectrometry (MS), gas chromatography (GC) and the two in tandem in the detection and analysis of narcotics and explosives is well established, but the methods are becoming more refined and being applied in association with portable systems. The latter is achieving growing popularity in spite of drawbacks.
Mobile screening systems, in the case of the on-site detection of explosives and chemical agents can include smartphones apps, or chemical/explosive detectors worn as badges by military personnel with results cross-referenced by Cloud-based databases. Larger-scale portable devices can be used in the field and are capable of some analysis.
For example, devices produced by Smiths Detection and newly devised systems such as an artificial sniffer for the security market with enhanced detection, developed by the University of Liverpool, UK, as part of the EC project CHEMSNIFF. However, whereas speed of detection can be vital in time-critical situations, lab-based analysis continues to be the essential means whereby in-depth analysis can be achieved for legal as well as purely scientific reasons.
Dr Trisha Conti, of the Vermont Forensic Laboratory in the USA, says, in relation to narcotics, “It seems as though many of the portable systems are used by narcotic officers as screening devices. Validation of these systems according to accreditation (ASCLD/LAB, ISO17025) and discipline-specific (SWGDRUG) standards have not been performed. That limits their usefulness as confirmation tools leaving conventional laboratory analysis as a requirement since it’s defendable in court. I believe there may be labs using hand-held Raman systems after validation, but still referring to them as screening tests.”
Dr Michal Kirchner, late of the Institute of Analytical Chemistry at Slovak University of Technology agrees that chromatography systems are not likely to be used directly to analyse (in this case) explosives when the result is needed in a short timeframe. “But the use of MS in combination with GC can be and indeed is used in forensic science and as a method for obtaining legal evidence and can be used in evaluation of newer detection systems.”
Gas and mass
Dr Warren Mino of Smiths Detection comments, “GC/MS is the gold standard in chemical detection. It is used in many industries beyond defence, including ener0o9p9gy and pharma. Its highly accurate technology is relied upon by chemists and scientists across the world.
“Combining GC and MS measures a sample with two different analytical techniques that can together confirm their individual results.
Because GC measures the retention time of the chemical and MS produces results that can be compared with a mass spectral database, combining both technologies helps to reduce the occurrence false positives.
One of the most powerful characteristics of the combination of GC and MS is its ability to separate the sample into its individual components. For example, diesel fuel has many compounds that could mask a threat, but GC/MS has the ability to detect and identify individual traces of threats, even in a high-intensity complex background.”
Kirchner believes the advantage of GC is that it provides much higher resolution, which provides a higher degree of confidence that the detected compound is accurately identified, while the use of MS provides an even higher degree of confidence as it provides detailed information on molecular structure. Conti, meanwhile, notes the advantages of GC/MS analysis include mixture separation, speed of analysis and production of reproducible spectra. However, she identifies one disadvantage: trouble identifying some positional and regioisomers. “This is where IR [infra-red spectrometry] analysis is beneficial,” she says.
In Vermont Forensic Laboratory research Conti and her team looked into recent improvements in GC/IR as providing a simple alternative or supplemental approach to GC/MS for the identification of certain compounds: a new instrument was introduced to collect GC effluent on a liquid-nitrogen cooled, IR transparent window, enabling direct analysis of the deposited solid material. This technique proved superior to the IR light pipe in sensitivity, IR spectral quality, and allowed direct comparison of the collected spectra to existing IR databases.
The research focused on the routine identification of commonly encountered drugs, designer drugs, closely related drug isomers, as well as the fundamentals of the GC and IR systems, the team reported. “The research was undertaken to develop this technology into a viable technique for the forensic community.” The instrument proved to be a powerful forensic tool providing complimentary data to GC/MS.
For the purpose of explosive detection on-site (for instance, a crime scene or security checkpoint) Kirchner concedes that Ion Mobility is better suited: “It is superior in short time analysis (seconds) with no need of sample preparation.” However his team’s method is capable of providing quantitative analysis (how much of the explosive was present). “Our method would be used for evaluation of the potentially new developed system.”
In their research the team employed fast GC with electron capture detector (GC-EDC) and fast GC with quadrupole mass spectrometry detector (QMS) to improve the detectability of tested explosives.
They found that the energy of electrons for EI ionization had no significant influence on the detectability of the searched explosives. “In the case of ECD utilized for detection, significant band broadening was observed in the cell of the detector and increase of auxiliary gas flow rate had no positive effect on the peak shapes.”
Although GC separation of polar explosives is affected by their adsorption in the chromatographic system, which results in decreased response and peak tailing, the team found the application of analyte protectants lowered the degree of explosives adsorption in the system greatly. This resulted in improved peak shapes and linearity of response.
The use of GC and MS is a preferred method in chemical detection and analysis. GC-MS combines the features of both to identify different substances within a test sample.
Applications include drug detection and explosives analysis. Furthermore, the combination of GM, MS, GM/MS and other technology is taking laboratory analysis forward, so refining scientific testing and the better isolating of target elements from background disturbance. These advances may not be regarded as newsworthy as the novel miniature systems deployed in the field, but the hard-nosed in-laboratory progress is not only fundamental to in-depth analysis, but key to all associated technology.
Dr Natalie Mai, a research fellow at Cranfield University in the UK, uses GC-MS to analyse the gases coming from the decompositions of explosives and the identification of the components of explosives.
She explains her ongoing work in this area: “We use GC-MS to understand the mechanism of degradation of ageing explosives. For example, nitrocellulose (NC) thermally degrades over time liberating gases such as NOx, a mixture of NO and NO2. The study of these gases allows us to investigate the ageing mechanisms of NC-based formulation.”
She adds: “Unfortunately with the column we are using we cannot detect NO2 but we definitely observe NO and N2O. The detector we are using is a single quadrupole mass spectrometer.”