Murphy, Bronagh Ruth

English

Forensic Scientists need to be able to detect, and confidently identify, any explosive substance encountered during forensic casework. This means flexible analytical methods that provide comprehensive detection of explosives, their precursors, transformation products and related compounds are required. Existing analytical methods typically only target the most commonly encountered explosive substances and often cover relatively small sets of structurally related compounds. Liquid chromatography coupled to high resolution mass spectrometry (LC-HRMS) is emerging as a viable technique in many fields for screening, identification and quantification of larger numbers of compounds. The aim of this thesis is to investigate the suitability of LC-HRMS for screening and identification of large numbers of known, unknown and suspect energetic materials. An LC-HRMS method was developed and the chromatographic separation and ionisation conditions were optimised for a set of eighteen initial target analytes including nitroaromatics, nitramines, nitrate esters and peroxides. The method performance was then assessed for a larger number of target analytes to investigate the potential for suspect screening and non-target analysis of additional energetic materials without further optimisation. The effect of different identification criteria, such as mass accuracy thresholds, number and type of ions and retention time windows, on selectivity and sensitivity was also examined, to support the selection of evidence-based identification requirements for LC-HRMS analysis of energetic materials. Finally, retention time prediction was investigated for the potential to aid preliminary identification of suspect or non-target energetic materials by prioritising acquisition of reference materials or excluding isomers. Overall, generalisability of a developed LC-HRMS method to a larger set of energetic materials, including MEKP, nitrated sugars and organic gunshot residues, was demonstrated for the first time. This supported the use of full-scan LC-HRMS, for suspect screening and non-target analysis of energetic materials. However, even with high resolution and mass accuracy it was not always possible to unequivocally identify energetic materials using LC-HRMS, due to the presence of hundreds or even thousands of isomers in some cases. In-source fragment ions and the use of ion ratios, increased selectivity but at a cost of sensitivity. The LC-HRMS method was successfully applied to the detection of explosives in contact traces and on passive vapour samplers. The retention time prediction models and prediction intervals presented in this thesis showed promise for adding value to suspect or non-target screening of energetic materials. Following a critical evaluation of the use of LC-HRMS, alone and in combination with other techniques, good chromatographic separation and tandem mass spectrometry are recommended for confirmatory analysis, along with a consideration of the number of isomers for individual compounds. Due to compromises in selectivity or sensitivity, identification criteria will likely differ for screening versus confirmatory analysis

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Suspect screening and identification of energetic materials using liquid chromatography coupled to high-resolution mass spectrometry

https://kclpure.kcl.ac.uk/portal/files/116619185/2019_Murphy_Bronagh_1238920_ethesis.pdf

Suspect screening and identification of energetic materials using liquid chromatography coupled to high-resolution mass spectrometry

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