Dr Patrick Sears

Direct analyte probed nanoextraction (DAPNe) is a technique that allows extraction of drug and endogenous compounds from a discrete location on a tissue sample using a nano capillary filled with solvent. Samples can be extracted from a spot diameters as low as 6 µm. Studies previously undertaken by our group have shown that the technique can provide good precision (5%) for analysing drug molecules in 150 µm diameter areas of homogenised tissue, provided an internal standard is sprayed on to the tissue prior to analysis. However, without an isotopically labelled standard, the repeatability is poor, even after normalisation to and the spot area or matrix compounds. By application to tissue homogenates spiked with drug compounds, we can demonstrate that it is possible to significantly improve the repeatability of the technique by incorporating a liquid chromatography separation step. Liquid chromatography is a technique for separating compounds prior to mass spectrometry (LC-MS) which enables separation of isomeric compounds that cannot be discriminated using mass spectrometry alone, as well as reducing matrix interferences. Conventionally, LC-MS is carried out on bulk or homogenised samples, which means analysis is essentially an average of the sample and does not take into account discrete areas. This work opens a new opportunity for spatially resolved liquid chromatography mass spectrometry with precision better than 20%.

This thesis explores the feasibility of testing for drugs from a fingerprint. Previous publications have reported drug detection in fingerprints from either drug users or after contact with a substance. There are possibilities to exploit these findings either for forensics (where a finger-mark is deposited at a crime scene to give intelligence about a donor) or for drug testing (where fingerprints are deposited under controlled conditions). In forensic science, it may be sufficient to know that a drug has been either handled or ingested within a specific time frame. In contrast, for drug testing, it may be necessary to exclude handling of drugs as a possible source. In either case, it is necessary to understand the significance of detecting a drug or its metabolite in a fingerprint. This thesis explored the significance of detecting a selection of illicit drugs in fingerprints. In Chapter 4 and Chapter 5, a rapid analysis method based on paper spray high resolution mass spectrometry is developed and validated for cocaine and its metabolite, benzoylecgonine (BZE), and the method is applied to the fingerprints of non-drug users and drug users respectively. As a result, cocaine and BZE were found in samples from both non-drug users (set as environmental cut-off) and drug users. The detection rate from drug users was above 90 % and there were no false positive using this method. Moreover, handwashing involvement became indicative of either ingestion of cocaine OR recent contact with cocaine. In Chapter 6 and 7, imaging mass spectrometry techniques were employed to determine whether contact and ingestion scenarios can be distinguished via spatial distribution of analytes. Those results supported the hypothesis that hot spots would be formed in fingerprints after contact whereas analytes would be evenly distributed in fingerprints after ingestion. The presence of BZE was also used to in distinguishing fingerprint samples from the two scenarios. In Chapter 8 and 9, the paper spray mass spectrometry methodology was expanded to a selection of novel psychoactive substances (NPS) relevant to a prison environment using fingerprints for the first time. The method was applied to the fingerprints of prisoners before and after participants washed their hands. As a result, NPS substances were not detected from any participants, in agreement with their urine testing. Finally, in Chapter 10, the data collected in Chapter 4 and 5 was analysed retrospectively for detection of heroin and 6-AM in fingerprints to explore the possibility of carrying out an untargeted analysis. The sensitivity of the method was not as good as for cocaine and benzoylecgonine (BZE), which led to the lower detection rate of heroin and 6-AM than that of cocaine and BZE. However, this study proved that the paper spray method could still provide qualitative and quantitative results of heroin detection in fingerprints. This study demonstrates that in the future with a suitable, deployable high resolution mass spectrometer, paper spray mass spectrometry could be used to detect cocaine, its metabolites and NPS for evidential purposes within the confines of a police station.

Paper spray mass spectrometry is a rapid and sensitive tool for explosives detection but has so far only been demonstrated using high resolution mass spectrometry, which bears too high a cost for many practical applications. Here we explore the potential for paper spray to be implemented in field applications with portable mass spectrometry. This involved (a) replacing the paper substrate with a swabbing material (which we call “swab spray”) for compatibility with standard collection materials; (b) collection of explosives from surfaces; (c) an exploration of interferences within a ± 0.5 m/z window; and (d) demonstration of the use of high-field assisted waveform ion mobility spectrometer (FAIMS) for enhanced selectivity. We show that paper and Nomex® are viable collection materials, with Nomex providing cleaner spectra and therefore greater potential for integration with portable mass spectrometers. We show that sensitive detection using swab spray will require a mass spectrometer with a mass resolving power of 4000 or more. We show that by coupling the swab spray ionisation source with FAIMS, it is possible to reduce background interferences, thereby facilitating the use of a low resolving power (e.g. quadrupole) mass spectrometer.

In this publication we work towards providing fast, sensitive and selective analysis of explosive compounds collected on swabs using paper spray mass spectrometry. We have (a) increased the size of the paper spray substrate to 1.6×2.1 cm for compatibility with current practise in swabbing for explosive material; (b) developed a method for determining a successful extraction of analyte from the substrate to reduce false negative events; and (c) expanded the range of analytes that can be detected using paper spray to include the peroxide explosive HMTD, as well as nitroglycerine (NG), picric acid (PA) and tetryl. We report the development of a 30 s method for the simultaneous detection of 7 different explosive materials using PSMS with detection limits below 25 pg, as well as detection of HMTD at 2500 pg, showing an improvement on previously published work.