The Routine Integration of Raman Spectroscopy into the Forensic Examination of Black Cotton

Transcription

1 The Routine Integration of Raman Spectroscopy into the Forensic Examination of Black Cotton Felicity S. Koens Bachelor Of Forensic Studies (Forensic Science) National Centre for Forensic Studies (NCFS) University of Canberra, ACT 2601 A thesis submitted in partial fulfillment of the requirements for the degree of Bachelor of Applied Science (Honours) at the University of Canberra 18 th June 2013

2 Acknowledgements The completion of this thesis would not have been possible without the continued support from a number of people in my life. Firstly, I would like to express my gratitude towards my primary supervisor, Professor James Robertson. Thank you for mentoring me through my honours experience, and providing me with every opportunity to develop my knowledge base in the field of forensics. This had been an invaluable experience, of which I am exceptionally appreciative. I would also like to thank Dr Jane Hemmings, my secondary supervisor, for educating me in all things Raman. Without your generosity of knowledge and patience, this project would not have been possible. Thank you to Dr Vincent Otieno-Alego, for repairing the Raman on the days it was experiencing technical issues, thereby keeping my experimental work on track. To Professor Chris Lennard, thank you for sharing your knowledge in Hyperspectral Imaging and MSP. Thank you to the Australian Federal Police and in particular the chemical criminalistics team, for giving me access to the Raman Instrument and providing me with great company and support on my experimental days in Weston. Words will not be able to express the appreciation I feel towards all the honours students who have shared office 7D3 during my time completing honours. I extend towards you all, my utmost gratitude for the encouragement, company and most importantly, the laughs. In particular I d like to thank Rory, for providing me with endless entertainment, and a friendship that will last a lifetime. To my partner James, who I was so fortunate to meet through this honours course. Thank you for your persistent advice, positive reinforcement and unconditional love. Finally to my family, your unrelenting love and encouragement from the very beginning has given me the determination and confidence to work as hard as I possibly could. To my twin sister Erin, you have been a constant source of strength for me and truthfully, your tremendously thoughtful daily pep talks will be memories I will cherish forever. Page iii

3 Abstract Trace materials often establish the most physical information of a crime. Textile fibres have long been recognised as being able to provide important evidential information and are the most frequently encountered type of trace evidence recovered in relation to crime. A well established sequential examination protocol has been developed for the examination of fibres. This is based on microscopy of fibres mounted on glass slides with a suitable mountant and a glass cover slip. In this protocol, fibres are both identified and features such as colour are observed. Comparison microscopy is also conducted between recovered fibres and fibres from known sources. However, for some examinations, especially of manmade fibres, fibres may have to be removed from the mountant for examination such as is the case with FTIR. In an ideal examination protocol, it would be desirable to gain the maximum information from mounted fibres. With respect to Raman spectroscopy, this has proven to be a useful tool in the identification of fibres and that analysis of their dye components. However, its implementation into the general routine protocol of fibre dyes has not yet been completely incorporated by laboratories. This is partly due to variations in the way fibres are presented to the instrument. For Raman spectroscopy, it is common practice to demount the fibre and suspend it over tape on an aluminium covered slide. This can pose a serious risk for recovered evidence, as there is potential for loss of sample, particularly where small fibres like cotton are concerned. The chemicals used to dissolve the mountant, so that fibres can be recovered, may also have adverse effects on the fibre dye or substrate. It would be highly desirable, to keep the fibres mounted on glass under a glass cover slip. Not only would evidence be maintained, but also sample preparation would be reduced, thereby increasing the efficiency of fibre examinations. Hence the primary focus of this study was to examine the effect that glass and mountant have on Raman spectroscopy and whether a meaningful Raman spectrum can be obtained from mounted fibres. This was a baseline study, in which Raman spectra were interpreted at the raw data level for visual differences. Using a Renishaw InVia Reflex Raman Microscope with a 785nm laser attachment, successful Raman spectra were obtained from samples mounted on glass. This was dependent upon a number of factors including dye shade and focal position. Page iv

4 Table of Contents Certificate of Authorship... ii Acknowledgements... iii Abstract... iv Table of Contents... v List of Figures... viii List of Tables... x Chapter 1. Introduction Forensic Relevance of Textile Fibres Textile Fibres Fibre Classification Fibre Frequency Cotton Properties Methods of Fibre Recovery Hand Retrieval Tape Lifting Scraping Vacuuming Systematic Analysis of Textile Fibres Microscopy Polarizing Light Microscopy (PLM) Fourier Transform Infrared (FTIR) Other Optical Techniques Pyrolysis Gas Chromatography (Py-GC) Raman Spectroscopy Colour and Fibre Dye Basic Theory of Colour Fibre Dyes and Pigments Reactive Dyes Types of Reactive Dyes Application of Reactive Dyes onto Cotton Sulphur Dyes Dye Photodegradation Systematic Detection of Dye Comparison Microscopy Microspectrophotometry (MSP) Dye Extraction and Thin Layer Chromatography (TLC) Raman Analysis in the Systematic Detection of Dyes Raman Spectroscopy Raman Theory Basic Instrumentation Page v

5 Forensic Application of Raman Spectroscopy Limits of detection and Varying Wavelengths Sample Preparation and Mountant Advanced Raman Techniques Summary Project Aims Chapter 2. Materials and Method Material Black/Grey Cotton Database Shade Variation Database Sub Sampling and Mounting Methods Black/Grey Cotton Database Shade Variation Database Mounting Methods for Examination Glass and Entellan Mounting Method Aluminium Bridge Mounting Method Raman Method Renishaw InVia Reflex Raman Microscope Software Instrumentation Set-Up Instrument performance Test Analysing the Polystyrene Standard Analysing the Red Acrylic Standard Analysing the Black/Grey Cotton Database and Shade Variation Database Aluminium Foil Mounted Samples Glass and Entellan Mounted Samples Hyperspectral Imaging Method PARRISS Analytical Hyperspectral Imager Software Instrumentation Set Up Instrument Performance Test Analysing a Sample Chapter 3. Results Raman Results Discrimination Power of Raman Glass Mounting Method for the Black/Grey Cotton Database Dye Intensity Focal Position Glass Mounting method for the Shade Variation Database No Sun exposure Sun Exposure Page vi

6 3.2. Hyperspectral Imaging Results Discriminatory Power of MSP MSP spectra of the Shade Variation Trial Database Hyperspectral Imaging Feature Analysis of both Raman and MSP Combined Discriminatory Power for the Black/grey Cotton Trial Database Chapter 4. Discussion and Conclusion References Appendix 1. Sample List... A1 Appendix 2. Blank sample Raman spectra... A21 Page vii

7 List of Figures Figure 1.1. Classification of fibres with examples (Robertson and Grieve 1999)... 3 Figure 1.2. Frequency of colour/generic class combination (n = 3025) (Cantrell et al 2001)... 4 Figure 1.3. Electromagnetic spectrum (York University online 2012)... 9 Figure 1.4. Simple energy transitions for Rayleigh and Raman scattering ( 14 Figure 1.5. Black cotton through glass cover slip (Above). Black cotton with no cover slip (Below) (Hemmings 2012) Figure 2.1. Glass and entellan mounting method Figure 2.2. Aluminium bridge mounting method Figure 3.1. Raman Groupings Figure 3.2. Example Raman spectrum from Group A Figure 3.3. Example Raman spectrum from Group B Figure 3.4. Example Raman spectrum from Group C Figure 3.5. Example Raman spectrum from Group D Figure 3.6. Example Raman spectrum from Group E Figure 3.7. Example Raman spectrum from Group F Figure 3.8. Example Raman spectrum from Group G Figure 3.9. Raman spectra of sample (glass) and (aluminium) Figure 3.10 Raman spectra of sample (glass) and (aluminium) Figure Raman spectra of sample (glass) and (aluminium) Figure Raman spectra of sample (glass) and (aluminium) Figure 3.13 Raman spectra of samples (glass) and (aluminium). Corresponding original garment image attached Figure Raman spectra of samples (glass) and (aluminium). Corresponding original garment image attached Figure Sample Raman spectrum and corresponding microscope image of a black cotton fibre mounted on aluminium foil Figure Sample Raman spectrum and corresponding microscope image of a black cotton fibre mounted on glass - Focal position Figure Sample Raman spectrum and corresponding microscope image of a black cotton fibre mounted on glass - Focal position Figure A black cotton swatch showing significant photodegradation over approximately a 3 month period of sun exposure Page viii

8 Figure Raman spectra of samples (glass) and (aluminium). No sun exposure or laundering Figure Raman spectra of sample (glass) and (aluminium) after approximately 3 months sun exposure Figure Raman spectra of sample (glass) and (aluminium) after approximately 3 months sun exposure Figure MSP frequency of spectra and the respective grouping Figure Example of MSP spectrum from Group Figure Example of MSP spectrum from Group Figure 3.25 Example of MSP spectrum from Group Figure Example of MSP spectrum from Group Figure Example of MSP spectrum from Group Figure Example of MSP spectrum from Group Figure Sun exposure vs No sun exposure spectra Figure Intensity differences from the Sun exposure sample set Figure Saved Master spectra Figure 3.32 First example of the hyperspectral images viewed Page ix

9 List of Tables Table 1.1. Percentage of different garments made of 100% cotton (Grieve, Biermann and Davignon 2001) Table 2.1. Raman InVia Specifications Page x