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Title: Development of in situ mass spectrometry analysis techniques for the forensic investigation of trace evidence
Author: Rankin-Turner, Stephanie
Awarding Body: Loughborough University
Current Institution: Loughborough University
Date of Award: 2019
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The analysis of biological fluids, such as blood and semen, discovered during the investigation of a potential crime can provide police forces with essential information to aid their investigation. However, many of the techniques for body fluid identification are not ideally suited to the analysis of potential evidence, being non-specific, destructive and expensive. Although individual presumptive tests are relatively inexpensive, the need to perform multiple tests on suspected biofluids can rapidly increase overall analysis costs. Furthermore, the use of presumptive tests typically involves the addition of test reagents to suspected biofluids, ultimately contaminating potential forensic evidence. The use of non-specific presumptive tests conducted at a crime scene often involve laboratory-based confirmatory tests, increasing the time taken for police to positively identify a suspected body fluid. Furthermore, there is currently no established method for estimating the age of a body fluid, thus police have no way of knowing if the sample is relevant to the investigation. In recent years analytical techniques such as mass spectrometry have been increasingly applied to forensic body fluid analysis. However so far suitable techniques for the identification and age estimation of body fluids have not been established. This research aims to develop mass spectrometric techniques for the in situ identification and age estimation of biological fluids, in addition to the direct analysis of other types of forensic evidence, specifically fingerprints and condoms. The research presented in this thesis demonstrates the possibility of utilising direct mass spectrometry techniques for the identification of human body fluids based on their unique chemical profiles. The Desorption-of-Surface (DOS) probe was developed, a handheld device designed to thermally desorb volatile compounds from surfaces using a stream of heated N2. This technique enabled volatile organic compounds to be sampled from body fluids in-situ and drawn into the mass spectrometer for rapid analysis. Using this technique, the chemical profiles of blood, saliva, urine and semen were found to be sufficiently distinct to enable differentiation between different body fluids and possible contaminants (for instance, food and cosmetic products that could be encountered during the investigation of a crime scene). Furthermore, previous research has demonstrated that chemical changes occur in deposited biological fluids over time as a result of environmental exposure, for instance the loss of components to the environment or the formation of new analytes over time. These chemical differences open the possibility of estimating the age of a body fluid based on its chemical profile. Similarly, DOS probe was also applied to the analysis of fresh and aged fingerprints, showing the possibility of detecting time-dependent differences in fingerprint residues that could, given further investigation, be used to develop a fingerprint age estimation method. With a focus on less volatile analytes, sheath flow probe electrospray ionisation mass spectrometry was developed. The sfPESI probe is a simple construction which, when briefly applied to the surface of a wet or dry sample, forms a liquid microjunction to enable analyte extraction. Upon application of a high voltage to the probe, an electrospray is formed. This technique offers an extraction and analysis time of less than 10 seconds per sample. The probe enabled the surface analysis of fresh and aged biological samples, applicable to a range of porous and non-porous surface materials. The technique was furthermore applied to the analysis of sexual assault evidence in the form of condoms. By applying sfPESI to the surface of different condom types, unique chemical profiles were produced, demonstrating the potential to detected prophylactic use based on mass spectral profiles. The techniques developed in this thesis facilitate the in situ analysis of biological samples, enabling rapid sample analysis whilst necessitating no sample preparation and preserving the integrity of the sample. All of these considerations are important in the development of analytical tools for on-site analysis in forensic science. The development of these rapid analysis techniques could provide police forces with a non-destructive way of confirming the identity of a suspected body fluid at the scene, and even estimating how long the stain has been there to quickly establish its relevance to the investigation.
Supervisor: Not available Sponsor: EPSRC
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: mass spectrometry ; ambient ionisation ; forensics ; volatile organic compounds ; body fluids ; surface analysis