X-ray Scattering and Chemometrics as Tools to Assist in the Identification of Gunshot Residues by Wavelength Dispersive X-ray Fluorescence Spectrometry

Wavelength dispersion X-ray fluorescence spectrometry (WDXRF) is a non-destructive technique and therefore attractive for gunshot residues (GSR) analysis. It is well known for determination of inorganic constituents of samples. However, X-ray scattering region spectral data is not commonly used, although it may provide information about organic constituents and their interactions. This work employed X-ray scattering region and inorganic elements spectral data for a better characterization of GSR. Swabs containing residues collected from the hand of people who fired (shooters group) and also from the hands of people which did not fire (control group) with guns were analyzed directly by the WDXRF. Brake pad and people who perform activities that favor the accumulation of characteristic elements of GSR on their hands were chosen to compose the control group. Principal components analysis (PCA) discriminated the GSR according to the firearm/cartridge used. However, similar GSR clustering did not occur without X-ray scatter data, showing the importance of X-ray scattering spectrum for GSR evaluation. The k-nearest neighbors (k-NN) method correctly classified all samples from shooters and control groups, employing from 1 to 5 nearest neighbors. No anomalous behavior was detected by PCA and hierarchical cluster analysis (HCA).

波长色散X射线荧光光谱法（Wavelength dispersion X-ray fluorescence spectrometry, WDXRF）是一种无损检测技术，因此在枪支残留物（gunshot residues, GSR）分析领域极具应用吸引力。该方法凭借对样品无机组分的精准测定而广受认可。然而，尽管X射线散射区光谱数据能够提供有机组分及其相互作用的相关信息，但这类数据的应用却并不普遍。本研究结合X射线散射区光谱与无机元素光谱数据，以实现对枪支残留物的更全面表征。研究人员直接采用波长色散X射线荧光光谱法，对两类拭子样本进行分析：一类采自持枪射击者的手部（射击组），另一类采自未持枪射击者的手部（对照组）。对照组样本涵盖刹车片样本，以及日常手部易积累枪支残留物特征元素的人员样本。主成分分析（Principal components analysis, PCA）可根据所用枪支/弹药筒对枪支残留物样本进行有效区分。但若未引入X射线散射数据，则无法实现相似枪支残留物样本的聚类，这凸显了X射线散射光谱在枪支残留物评估中的重要价值。采用k近邻（k-NN）方法，选取1至5个近邻样本时，可对所有射击组与对照组的样本实现正确分类。主成分分析与系统聚类分析（hierarchical cluster analysis, HCA）均未检测到异常样本行为。