This thesis focuses on the detection of threat agents, i.e. explosives and new psychoactive substances (NPS) using SRI-ToF-MS (Selective Reagent Ionisation-Time of Flight-Mass Spectrometry). This is a novel technology, able to detect trace gas compounds with high sensitivity, high selectivity and virtually in real time. While its ability to detect volatile organic compounds (VOCs) in a wide range of fields has already been demonstrated, there has only been a small amount of research into homeland security applications.
The interest in the field of homeland security has been raised by the increased risk of terrorist activities in recent years. Drug use also poses significant challenges to society. A study from the United Nations Office of Drugs and Crime (UNODC) has identified the increase in the number and rate at which New Psychoactive Substances (NPS) are legally entering the market as one of the most notable trends in drug markets over the last 5 years. These substances represent an obvious risk, as their effects on health are mostly unknown.
The present thesis involves a detailed study on 10 NPS using SRI-ToF-MS. No previous investigations of NPS involving this analytical technique had been carried out. Hence, for each of these substances (mostly recreational stimulants) both, mass spectra at standard operational conditions and complete E/N studies (i.e. dependence of the product ion branching ratios on the ratio between the electric field, E, and the gas number density, N) are recorded. Furthermore, the product ion branching ratios at selected E/N values are used to identify the composition of an unknown mixture, i.e. a commercial NPS blend of unknown composition legally available online under the branded name “synthacaine”.
One of the major limitations of classic Proton Transfer Reaction-Mass Spectrometry (PTR-MS) is the ambiguousness in compound identification, as it relies solely on m/z values (i.e. the mass-to-charge ratio) of the product ions. Therefore compounds with very similar m/z values (or, in case of isomers, compounds with the same exact masses) cannot be distinguished and identified. In order to increase the selectivity of the analysis in SRI-MS different reagent ions, i.e. NO+, O2+ and Kr+ may be used in addition to H3O+, and their reactions pathways may be investigated. As an example, the possibility of distinguishing between two isomeric substitutes of the popular, but now widely controlled NPS mephedrone, is provided.
Since a lack of information on the time necessary when switching between different reagent ions, e.g. from H3O+ to O2+ and from H3O+ to NO+ was identified, this is investigated together with the different reaction pathways taking place when both of these reagent ions are reacting with some explosives, i.e. 2,4,6-trinitrotoluene (TNT), 1,3,5-trinitrobenzene (TNB), pentaerythritol tetranitrate (PETN) and cyclotrimethylenetrinitramine (RDX).
It is known that TNT shows an unusual E/N dependence, which could be used to rapidly identify this compound within a complex chemical environment. Therefore, extensive studies are carried out on picric acid (C6H3N3O7), a trinitroaromatic compound with a similar structure to TNT to verify whether this shows the same unusual E/N behaviour. In addition, the E/N dependence of the charged parent ion at several drift tube relative humidity levels is evaluated.