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Discrimination of Types of Thermal Sensitive Paper by Characterization of the Inorganic Additives by Fourier Transform Infrared Microscopy, Confocal Raman Microscopy, and Scanning Electronic Microscope-Energy Dispersive Spectroscopy

Identification of thermal sensitive paper is of importance to forensic scientists in the document examination and file source identification. Spectral methods, including infrared spectroscopy, Raman spectroscopy, and energy dispersive spectroscopy have been proven to be accurate and rapid in the investigation of numerous compounds in many studies; therefore, an optimized spectral method was introduced to discriminate the thermal sensitive paper with these instruments in this study. Seventeen samples from different manufactures and markets were collected and analyzed. The results indicated that paper samples could not be discriminated effectively by the organic ingredients (leuco, developer, sensitizer, lubricant, or adhesive). However, based on the difference of the inorganic additives (calcined Kaolin, calcium carbonate, titanium dioxide, and talc), the identification could be more easily realized by their IR characterization. The indicative peaks of the additives in IR and Raman spectra are summarized and tentatively explained. Energy dispersive spectroscopy analysis could also provide indirect evidence of the presence of certain inorganic ingredients. The method using the three instruments in combination proved to be characteristic and accurate and could be applied to the cases relative to the thermal sensitive paper.