0 99% same polymer matrix E.g., Two tyres from different brands 1% difference in additives Remaining sample pyrolysed GC Polymer detected GC (compound separation) MS (compound identification) Thermal desorption of sample Minimal amount of sample needed Direct analysis (no sample preparation required) Better resolution of volatile compounds - including additives Py-GC/MS components: Pyrolyser Cryo-trap GC MS Polymeric product = Polymer matrix + Additives Manufacturers' additive preferences drive chemical variation between brands Analytical technique: Double-shot Pyrolysis-GC/MS Scene compare with Suspect's possession provide link between Suspect Crime scene Polymeric evidence found at a scene: Detects additives MS Compounds condensed at the column using cryo-trap with N then released at the same time 2(liq.) Advantages for forensic analysis Comparison of SS vs DS Supported by: Elution time (min) Relative intensity Figure 1. Total ion chromatograms of tyre rubber (tread). The numbered peaks are examples of the common compounds detected in tyres. Contacts: nieo326@aucklanduni.ac.nz https://www.linkedin.com/in/chloe-ieong/ Results for tyre rubbers Single-shot (SS) Py-GC/MS involves pyrolysis at a set temperature Double-shot (DS) Py-GC/MS involves thermal The DS-TD allows the detection of 3 additional desorption (TD) followed by pyrolysis (Py) additive compounds (Bold in Fig. 1) Isobutylamine: Rubber accelerator Cyclohexanethiol: Chemical intermediate, stabiliser 1,2-dihydro-2,2,4-trimethyl-quinoline: rubber antioxidant References: 1. PubChem. (n.d.). Isobutylamine. Retrieved 22 August 2023, from https://pubchem.ncbi.nlm.nih.gov/compound/6558 2. New Jersey Department of Health and Senior Service (2000) Hazardous substance fact sheet-Cyclohexanethiol. Retrieved 22 August 202, from https://nj.gov/health/eoh/rtkweb/documents/fs/0568.pdf 3. Nowicki, J., Jaroszewska, K., Nowakowska-Bogdan, E., Szmatoła, M., & Iłowska, J. (2018). Synthesis of 2,2,4-trimethyl-1,2-H-dihydroquinoline (Tmq) over selected organosulfonic acid silica catalysts: Selectivity aspects. Molecular Catalysis, 454, 94–103. https://doi.org/10.1016/j.mcat.2018.05.016 4. Lv, Y. (2020). Py-GC/MS analysis of tyre rubber in traffic accident cases. Australian Journal of Forensic Sciences, 52(3), 313–322. https://doi.org/10.1080/00450618.2018.1545869 5. Causin, V. (2015). Polymers on the Crime Scene: Forensic Analysis of Polymeric Trace Evidence. Springer International Publishing. https://doi.org/10.1007/978-3-319-15494-7 6. Canvas (2023). Images of the forensic scientist and car tyre DS-Py 2 3 8 5 6 DS-TD 4 1 7 2 3 5 6 — — SS-Py 2 3 8 5 — 6 — 1: Isobutylamine 2: Benzene 3: Toluene 4: Cyclohexanethiol 5: D-Limonene 6: Benzothiazole 7: 1,2-dihydro-2,2,4- trimethyl-quinoline 8: Styrene Rubber and plastic-like products are composed of polymeric materials. Wads from shotgun DOUBLE THE SHOT, DOUBLE THE GAIN Chloe Ieong Supervised by Sally Coulson and Mickayla Dustin Common Polymeric Products found at Crime Scenes Disposable gloves Rubber smears from tyres Road cone fragments Aim: Increased Discrimination by Analysis of Additives Background a. School of Chemical Sciences, University of Auckland b. The Institute of Environmental Science and Research Ltd Current analytical methods focus on the detection of only the polymer. Based on the prevelance of polymeric products they are frequently found at crime scenes. A technique that detects both polymers and additives will provide better discrimination. (b) (b) (a) 1 2 3 Tracing chemical clues: Additive analysis of polymeric products using Double-Shot Pyrolysis Gas Chromatography/Mass Spectrometry (Py-GC/MS) —