Identification of paper and influence of its homogeneity in forensic investigations by ICP-AES/MS and other non-invasive spectroscopic techniques

Abstract: The purpose with this thesis was to find out if ordinary office paper was homogenous throughout the sheet in context of organic and elemental content. Two different types of papers were also analyzed, paper towel and corrugated paperboard. The techniques used were NIR, FT-IR and Raman spectroscopy for the evaluation of organic contents, and ICP-AES/MS for the measurement of elemental composition and concentration. Spectrofluorometry was also utilized to establish if the content of optical brightener was homogenous in all paper types. The spectroscopic techniques didn’t require any sample preparation except for cutting the papers in pieces, according to their “geographical” place in the sheets. The ICP-AES and ICP-MS analyses required sample preparation in form of cutting the pieces and digesting each of them with acid and hydrogen peroxide in digestion bombs. After the digestion the samples were diluted with purified water. The results showed that NIR and spectrofluorometry couldn’t differentiate samples within one sheet of all paper types, although NIR made a distinction between the office paper samples. FT-IR on the other hand could distinguish between samples in one group from samples belonging to another group further away within same sheet. The elemental concentrations of sample pieces were also significantly different within same sheet of office paper, paper towel and corrugated paperboard. This elemental distinction could be made in both ICP-AES and ICP-MS. The results from Raman spectroscopy were unusable due to gained broad bands as spectra instead of peaks, the reason for that is high fluorescence. Different laser intensities were used with no change in result.