Investigation of ball point pen inks by capillary electrophoresis (CE) with UV/Vis absorbance and laser induced fluorescence detection and Particle Induced X-Ray Emission (PIXE)

In the process of examining fraudulent documents ink analysis is a small bu t important part of the operation of forensic laboratories. Systematic appr oaches to ink comparison and identification have been performed by optical methods and various chromatographic techniques. Capillary electrophoresis (CE), a relatively new separation technique with very high resolution power, and Particle Induced X-Ray Emission (PIXE) were used for the analysis of ball point pen inks. In comparison to water solub le fountain pen inks, ball point inks are less soluble or insoluble in wate r and these inks contain only few components. The study focused on the opti mization of the separation of ink extracts from paper material of commercia lly available inks with respect to resolution and analysis time. During the method development process different buffers, organic modifiers, and surfa ctants were tested. Good results were obtained with a 50 mM borate buffer p H 9.0 containing 50% acetonitrile. Reproducible extraction procedures as we ll as separations enables one to perform the quantification of the ink peak s within 1-8% standard deviation for parallel extractions of the same ink. Electropherograms of 20 inks of various origin showed patterns which were i n most cases distinctly different from each other. PIXE measurements with an external proton beam were used to determine the m etal composition. The ratio of the peak areas for copper and zinc as well a s differences in the elemental composition could be used to distinguished b etween the samples. No coincidence was observed between samples hardly distinguishable by elect rophoretic separations and by PIXE-measurements. Samples with nearly identi cal metal composition showed different peak pattern in the electropherogram s, and nearly identical electrophoretic behavior of two or more samples was accompanied by quite different copper/zinc-ratios or supplementary metals identified by PIXE.