Forensic discrimination of photocopy and printer toners I. The development of an infrared spectral library

Microscopical reflection-absorption by infrared spectroscopy (R-A IR) was shown as a viable technique for analyzing the polymer resins contained in dry, black photocopy and printer toners. The sampling technique involves a heat transfer of the toner from a document to the reflective surface of aluminum foil followed by analysis by R-A IR. The technique is simple, fast, and readily available to most forensic laboratories. A searchable spectral library was created that contains 807 toner samples analyzed by R-A IR. Ninety-eight groups were established based on spectral characteristics, and a flowchart was developed to assist with group assignments. A blind study was conducted to compare twenty photocopied documents each paired to a test document to determine if the pair could have been produced from the same copier. The analyst obtained 100% correct results in this study. Tests on thirty samples with the spectral library produced 90% first hits for the correct group. The three remaining samples were correctly determined by visual comparison of spectra for the top three hits. An actual case study was conducted where the investigation was narrowed from 400 possible machines to eight based on a comparative study of the photocopy toners.Electronic Supplementary Material Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s00216-003-2073-0This is publication number 03-02 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. This paper was presented in part as a poster at the International Symposium on the Forensic Examination of Trace Evidence in Transition, San Antonio, Texas, 24–28 June 1996.