Ieong Nga Weng Chloe, Dustin Mickayla, Coulson Sally
University of Auckland, School of Chemical Sciences, Private Bag 92019, Auckland 1142, New Zealand.
Institute of Environmental Science and Research (ESR), Private Bag 92021, Auckland 1142, New Zealand.
Forensic Sci Int. 2024 Nov;364:112238. doi: 10.1016/j.forsciint.2024.112238. Epub 2024 Sep 26.
Polymers are present in many different products, such as paints, plastics, and rubbers, which are routinely encountered in forensic casework. Comparison of such samples involves an initial visual examination followed by comparison of the chemical compositions of the exhibits. Techniques such as Fourier transform infrared spectroscopy (FTIR) and pyrolysis gas chromatography - mass spectrometry (PyGC-MS) have been reported for determining the chemical compositions of polymers in forensic samples. Double-shot pyrolysis gas chromatography - mass spectrometry (DS-PyGC-MS) is an extension of single-shot pyrolysis gas chromatography - mass spectrometry (SS-PyGC-MS) which is the current PyGC-MS method used in most forensic laboratories. DS-PyGC-MS involves a preliminary thermal desorption GC-MS step, followed by the pyrolysis GC-MS step, with this second step being analogous to SS-PyGC-MS. The pyrolyser furnace operates at a lower temperature during the thermal desorption step, allowing low volatility compounds, such as additives, to be thermally desorbed and detected, minimising interference from the polymeric component of the sample. This pilot study analysed four different polymeric substrates, commonly encountered in forensic casework, by DS-PyGC-MS. The substrates chosen were tyre rubber, road cones, cling film, and shotgun wads. The aim was to investigate whether more chemical information was generated by DS-PyGC-MS compared to SS-PyGC-MS, potentially providing increased discrimination of such samples. Qualitative results showed that tyre rubber and road cones were ideal substrates for DS-PyGC-MS. A wide range of additives were detected in these samples in the thermal desorption step, which were not detected using SS-PyGC-MS. All of the rubber tyres (n=5) and road cones (n=6) were able to be uniquely distinguished using DS-PyGC-MS. Some additional compounds were detected in the thermal desorption analysis of shotgun wads (n=4), providing increased discrimination compared to SS-PyGC-MS. For the cling film samples analysed (n=7) the polyethylene-based cling films (n=6) could not be distinguished from each other, with no compounds detected in the thermal desorption step. The other cling film sample contained a mixture of polylactic acid (PLA) and polybutylene adipate terephthalate (PBAT) and could easily be distinguished from the polyethylene-based cling films using either SS- or DS-PyGC-MS, or other common analytical methods such as Fourier transform infrared spectroscopy (FTIR). This pilot study has demonstrated that DS-PyGC-MS has the potential to provide more comprehensive chemical composition information for some polymeric substrates and is a promising method for the forensic comparison of polymer evidence.
聚合物存在于许多不同的产品中，如涂料、塑料和橡胶，这些在法医案件工作中经常遇到。对此类样品进行比较时，首先要进行目视检查，然后再比较物证的化学成分。傅里叶变换红外光谱法（FTIR）和热解气相色谱-质谱联用技术（PyGC-MS）等技术已被报道用于测定法医样品中聚合物的化学成分。双程热解气相色谱-质谱联用技术（DS-PyGC-MS）是单程热解气相色谱-质谱联用技术（SS-PyGC-MS）的扩展，而SS-PyGC-MS是目前大多数法医实验室使用的PyGC-MS方法。DS-PyGC-MS包括一个初步的热解吸气相色谱-质谱步骤，随后是热解气相色谱-质谱步骤，第二步与SS-PyGC-MS类似。在热解吸步骤中，热解炉在较低温度下运行，使低挥发性化合物（如添加剂）能够被热解吸并检测到，从而将样品中聚合物成分的干扰降至最低。这项初步研究通过DS-PyGC-MS分析了法医案件工作中常见的四种不同聚合物基质。所选择的基质是轮胎橡胶、路锥、保鲜膜和猎枪弹塞。目的是研究与SS-PyGC-MS相比，DS-PyGC-MS是否能产生更多化学信息，从而有可能增强对此类样品的区分能力。定性结果表明，轮胎橡胶和路锥是DS-PyGC-MS的理想基质。在热解吸步骤中，这些样品中检测到了多种添加剂，而使用SS-PyGC-MS未检测到这些添加剂。使用DS-PyGC-MS能够唯一区分所有橡胶轮胎（n=5）和路锥（n=6）。在猎枪弹塞（n=4）的热解吸分析中检测到了一些额外的化合物，与SS-PyGC-MS相比，区分能力有所增强。对于所分析的保鲜膜样品（n=7），基于聚乙烯的保鲜膜（n=6）彼此无法区分，在热解吸步骤中未检测到任何化合物。另一个保鲜膜样品含有聚乳酸（PLA）和聚己二酸丁二醇酯对苯二甲酸酯（PBAT）的混合物，使用SS-PyGC-MS或DS-PyGC-MS，或其他常见分析方法（如傅里叶变换红外光谱法（FTIR））都能很容易地将其与基于聚乙烯的保鲜膜区分开来。这项初步研究表明，DS-PyGC-MS有可能为某些聚合物基质提供更全面的化学成分信息，是一种用于聚合物物证法医比较的有前景的方法。
