The discrimination potential of diffuse-reflectance ultraviolet–visible–near infrared spectrophotometry for the forensic analysis of paper

The application of diffuse reflectance UV–VIS–NIR spectroscopy is proposed to differentiate 20 office paper samples, which had been deemed similar by a preliminary visual examination under several different lighting sources. The samples were firstly screened on the basis of the qualitative appearance of their spectra. A further discrimination was obtained by taking into account three parameters: the average reflectivity of the paper samples in the range 680–900 nm, and the integrated intensity of the absorption peak in the UV range at 272 nm and at 360 nm. The homogeneity of these parameters on both sides of the paper sheets was assessed, detecting a very uniform distribution of the optical brighteners. A special focus was posed on the determination of the discriminative power, in order to give a quantitative parameter on the proposed procedure, which is important when reporting results to the Court. The remarkable achievement of differentiating all the examined samples was obtained by UV–VIS spectroscopy, a very less expensive technique which is readily available in practically all forensic laboratories.