Separation, comparison and identification of fountain pen inks by capillary electrophoresis with UV-visible and fluorescence detection and by proton-induced X-ray emission

Abstract

The analysis of inks as a part of the detection of fraudulent documents is a small but important aspect of forensic science. The present study was focused on the separation of components of commercially available original fountain pen inks and on different paper substrates by capillary electrophoresis and proton-induced X-ray emission (PIXE). Electropherograms of inks from various manufacturers and countries separated in borate buffers with various methanol contents showed patterns which were in most cases distinctly different from one another. UV-Vis scans and fluorescence detection at different excitation and emission wavelengths have been used to compare similar mixtures and ink extracts from paper with the original ink composition, to identify concurrences or differences in the spectra of main and trace components and to improve the discrimination power of the technique in this way. Extraction conditions, like solvent composition, extraction time, paper carrier material, age of the ink and ink concentration have been examined with respect to signal intensity and the number of detectable components. PIXE spectra of ink samples on different paper substrates have been recorded to determine the elemental composition of the samples and to obtain additional information about the chemical composition of the dyes.