Analysis of forensic polymer samples using double shot pyrolysis gas chromatography – Mass spectrometry

IF 2.2 3区 医学 Q1 MEDICINE, LEGAL Forensic science international Pub Date : 2024-09-26 DOI:10.1016/j.forsciint.2024.112238
Nga Weng (Chloe) Ieong , Mickayla Dustin , Sally Coulson
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Abstract

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.
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使用双枪热解气相色谱-质谱法分析法证聚合物样本
聚合物存在于许多不同的产品中,如油漆、塑料和橡胶,这些产品在法医办案中经常会遇到。此类样本的比较包括初步的目视检查,然后比较证物的化学成分。据报道,傅立叶变换红外光谱法(FTIR)和热解气相色谱-质谱法(PyGC-MS)等技术可用于确定法证样本中聚合物的化学成分。双枪热解气相色谱-质谱法(DS-PyGC-MS)是单枪热解气相色谱-质谱法(SS-PyGC-MS)的延伸,后者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 GC-MS 步骤,然后是热解 GC-MS 步骤,第二个步骤与 SS-PyGC-MS 类似。在热解吸附步骤中,热解炉的工作温度较低,因此添加剂等低挥发性化合物可以通过热解吸附进行检测,最大程度地减少了样品中聚合物成分的干扰。这项试点研究利用 DS-PyGC-MS 分析了法医办案中常见的四种不同的聚合物基质。选择的基质包括轮胎橡胶、路锥、保鲜膜和猎枪弹。目的是研究与 SS-PyGC-MS 相比,DS-PyGC-MS 是否能产生更多的化学信息,从而提高对此类样品的鉴别能力。定性结果显示,轮胎橡胶和路锥是 DS-PyGC-MS 的理想基质。在热解吸步骤中,在这些样品中检测到了多种添加剂,而使用 SS-PyGC-MS 则检测不到这些添加剂。所有的橡胶轮胎(5 个)和路锥(6 个)都能用 DS-PyGC-MS 进行独特的鉴别。与 SS-PyGC-MS 相比,霰弹枪棉絮(4 个)的热解吸分析中检测到了一些额外的化合物,从而提高了分辨能力。在分析的保鲜膜样品(n=7)中,聚乙烯保鲜膜(n=6)无法相互区分,在热解吸步骤中未检测到任何化合物。另一种保鲜膜样品含有聚乳酸(PLA)和聚对苯二甲酸丁二醇酯(PBAT)的混合物,使用 SS 或 DS-PyGC-MS 或傅立叶变换红外光谱(FTIR)等其他常用分析方法可以很容易地将其与聚乙烯基保鲜膜区分开来。这项试验研究表明,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,是一种很有前途的聚合物证据法医对比方法。
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来源期刊
Forensic science international
Forensic science international 医学-医学:法
CiteScore
5.00
自引率
9.10%
发文量
285
审稿时长
49 days
期刊介绍: Forensic Science International is the flagship journal in the prestigious Forensic Science International family, publishing the most innovative, cutting-edge, and influential contributions across the forensic sciences. Fields include: forensic pathology and histochemistry, chemistry, biochemistry and toxicology, biology, serology, odontology, psychiatry, anthropology, digital forensics, the physical sciences, firearms, and document examination, as well as investigations of value to public health in its broadest sense, and the important marginal area where science and medicine interact with the law. The journal publishes: Case Reports Commentaries Letters to the Editor Original Research Papers (Regular Papers) Rapid Communications Review Articles Technical Notes.
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