Author: Eliza Moule
Moule, Eliza, 2020 An evaluation of direct sample analysis time of flight mass spectrometry for forensic analysis, Flinders University, College of Science and Engineering
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The emergence of ambient ionisation mass spectrometry has been driven by a need for high-throughput, accurate and flexible methods for analysis of a broad range of compounds. There are a broad range of techniques already developed and explored, including (but not limited to) Desorption Electrospray Ionisation (DESI) and Direct Analysis in Real Time (DART). Direct Sample Analysis Time of Flight (DSA-ToF) has not been comprehensively evaluated or explored as a competing technique in the ambient ionisation space. This work sought to evaluate the DSA-ToF as a technique for use in forensic science.
Optimisation of a broad method for the identification of MDMA, THC and cocaine demonstrated that there are substantial reproducibility issues with the instrument. Environmental contributions to signal variability were identified, with humidity, airflow and temperature fluctuations being responsible for large sinusoidal cycling in the signal response. Plasma cleaning was identified as necessary to remove organic matter contaminating the provided mesh that convoluted the low mass range. Quantification of the three drugs was possible but is not recommended. Limits of detection and quantification were able to be established but were not consistent when compared intra- and inter-day. This inconsistency would compromise the validity of any quantitative results.
Two methods were developed for the detection of THC, MDMA and cocaine from saliva, one involving a solvent extraction and the other involving a timed physical interaction of the saliva with mesh. The solvent extraction method allowed both qualitative and quantitative detection of the three drugs, although quantitative is not recommended. The timed-interaction method was suitable for qualitative identification only.
A further two applications were developed, involving the detection of nicotine, caffeine, caffeine metabolites and pseudoephedrine in breath. Uptake and elimination curves for these drugs were mapped across 2 hours from the breath of two volunteers. The detection of organic GSR components was also demonstrated, using a solvent extraction from the surface of adhesive GSR stubs. This solvent extraction was shown to not disrupt the inorganic particles present, and is suitable for integration into the existing GSR detection protocol (SEM-EDS identification of inorganic components).
Evaluation of this instrument indicated that it is capable of high-throughput, accurate screening of a broad range of samples in complex matrices. Environmental variables should be controlled by limiting air flow, temperature fluctuations, and humidity in the laboratory. Quantification can be performed but should not be relied upon as the only measure of content.
Keywords: ambient mass spectrometry, Direct Sample Analysis Time of Flight Mass Spectrometry, Breath analysis, saliva analysis, organic gunshot residue, illicit drug analysis
Subject: Forensic & Analytical Chemistry thesis
Thesis type: Doctor of Philosophy
Completed: 2020
School: College of Science and Engineering
Supervisor: K. Paul Kirkbride