Craig Adam
Faulds Laboratories, Department of Chemical and Forensic Sciences, Keele University, Keele, Staffs ST5 5BG, UK. E-mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Introduction

One of the aims in the forensic analysis of physical evidence is to compare a questioned material from a crime scene with a specific reference, for example from a suspect, to determine whether the two samples are indistinguishable. The examination of coloured materials such as inks and fibres falls into this category and presents a significant challenge to the forensic analyst who must determine whether the particular shades exhibited by the pair of samples may be discriminated or not.

There are two issues to be addressed in selecting the best technique for such work. First, how destructive of the sample is that analytical procedure, and second, is the comparison based on a quantitative interpretation of the data with objective criteria for the discrimination threshold? On this basis, the use of UV/vis spectroscopy has much to recommend it for the forensic examination of inks and fibres, though thin layer chromatography (TLC) is also widely used as a complementary method in both cases. The UV/vis spectrum directly quantifies the colour of the sample and the technique is reliable and fairly straightforward to carry out experimentally. Conventional UV/vis spectroscopy is destructive, though only very small quantities of material may be required. The advent of microspectrophotometry, however, means that non-destructive measurements may be made, for example, on a single fibre.

This short review will discuss first the forensic application of these techniques to fibres and then to ink evidence. In both cases, some of the chemometric methods used to interpret such spectra will be described, with the application of principal component analysis to ink spectra being covered in some detail.

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