| Affiliation: | (1) Department of Chemistry and Biochemistry, The University of South Carolina, Columbia SC 29208, USA;(2) Counterterrorism and Forensic Science Research Unit, FBI Laboratory, FBI Academy, Quantico, VA 22135, USA;(3) Questioned Documents Unit, FBI Laboratory, Quantico, VA 22135, USA;(4) Present address: Vertex Pharmaceuticals, 130 Waverly Street, Cambridge, MA 02139-4242, USA |
| Abstract: | Copy toner samples were analyzed using reflection-absorption infrared microscopy (R-A IR). The grouping of copy toners into distinguishable classes achieved by visual comparison and computer-assisted spectral matching was compared to that achieved by multivariate discriminant analysis. For a data set containing spectra of 430 copy toners, 90% (388/430) of the spectra were initially correctly grouped into the classifications previously established by spectral matching. Three groups of samples that did not classify well contained too few samples to allow reliable classification. Samples from two other pairs of groups were similar and often misclassified. Closer examination of spectra from these groups revealed discriminating features that could be used in separate discriminant analyses to improve classification. For one pair of groups, the classification accuracy improved to 91% (81/89) and 97% (28/29), for the two groups, respectively. The other pair of groups were completely distinguishable from one another. With these additional tests, multivariate discriminant analysis correctly classified 96% of the 430 R-A IR toner spectra into the toner groups found previously by spectral matching.This is publication number 03–03 of the Laboratory Division of the Federal Bureau of Investigation. Names of commercial manufacturers are provided for identification only, and inclusion does not imply endorsement by the Federal Bureau of Investigation. |
