Flynn Katherine, O'Leary Robyn, Lennard Chris, Roux Claude, Reedy Brian J
Centre for Forensic Science, University of Technology, Sydney, P.O. Box 123, Broadway NSW 2007, Australia.
J Forensic Sci. 2005 Jul;50(4):832-41.
This paper examines the potential of infrared chemical (hyperspectral) imaging as a technique for the forensic analysis of automotive paint chips in particular, and multicomponent (e.g., layered) samples in general. Improved sample preparation procedures for the infrared analysis of paint chips are detailed, with the recommendation that where mounting resins are chemically incompatible with the sample, it is better to mount and section the sample in a soft wax from which the sections can be removed and pressed into a KBr disk for transmission analysis. Infrared chemical images of multilayered paint chips have been successfully obtained, with the chief advantage over conventional infrared analysis being that thousands of infrared spectra are collected in a few minutes across the whole sample, at a spatial resolution of around 5 microm. As with conventional infrared spectroscopy, chemical species can be identified from their spectra, but the wealth of information available can be also extracted in a number of different ways that make multicomponent spectral (and hence chemical) comparisons between two samples easy to visualize and understand. In one approach, the infrared chemical images of two paint chips being compared side-by-side can be viewed as a "movie," in which each frame is an intensity map of the two samples at a given wavenumber (frequency) value. In another approach, the spectra (pixels) in the image files are classified into chemically similar groups, resulting in a "cluster" image that makes it possible to simultaneously compare all of the layers in two paint chips. These methods are applicable to other multicomponent samples, and also to other chemical imaging techniques.
本文探讨了红外化学（高光谱）成像技术在汽车漆片法医分析方面的潜力，特别是在一般多组分（如分层）样品分析中的应用。详细介绍了用于漆片红外分析的改进样品制备程序，并建议在固定树脂与样品存在化学不相容性的情况下，最好将样品固定并切片于软蜡中，然后从软蜡中取出切片并压制成KBr片用于透射分析。已成功获取多层漆片的红外化学图像，其相对于传统红外分析的主要优势在于，能在几分钟内以约5微米的空间分辨率在整个样品上收集数千条红外光谱。与传统红外光谱一样，可以从光谱中识别化学物质，但还可以通过多种不同方式提取丰富的可用信息，从而使两个样品之间的多组分光谱（进而化学）比较易于可视化和理解。在一种方法中，并排比较的两个漆片的红外化学图像可以看作是一部“电影”，其中每一帧都是两个样品在给定波数（频率）值下的强度图。在另一种方法中，图像文件中的光谱（像素）被分类为化学性质相似的组，从而生成一个“聚类”图像，使得可以同时比较两个漆片的所有层。这些方法适用于其他多组分样品，也适用于其他化学成像技术。
