Forensic discrimination of black laser prints by a combination of chemometric methods and μ-ATR-FTIR spectroscopy

The combination of spectral and chemometric methods to obtain information of the samples appears to be useful in forensic analysis of questioned documents. In this paper, the application of non-destructive method including FTIR spectroscopy in combination with principal component analysis (PCA) and multivariate analysis of variance (MANOVA) to differentiate black laser prints was investigated. A set of 49 types of laser printers of 10 brands was investigated. PCA was applied to identify the differences between the laser toner samples. PCA of laser prints spectra was used as a base of the method for toner identification. The difference between the spectra of the unknown print and the spectra of the database was tested. The method was confirmed by the analysis of four test prints. A model document printed on three different printers was prepared. The MANOVA test together with PCA scatter diagram confirmed that the model document was printed on three different printers.