Examination of black inkjet printing inks by capillary electrophoresis

Counterfeiting of documents is a common phenomenon in the modern world. A large proportion of forgeries relates to inkjet printed documents. Hence there is an evident need to develop an effective and reliable method for the differentiation and identification of inkjet inks on questioned documents. The aim of the presented study was to investigate the possibility of applying micellar electrokinetic capillary chromatography (MECC) to forensic analysis of inkjet inks extracted from black and white printouts.In order to achieve the above aim, a capillary electrophoresis system equipped with a diode array detector was used. The separation was performed using a fused silica capillary (60/50 cm total/effective length, 75 μm i.d.) with a background electrolyte composed of 40 mM sodium borate, 20 mM SDS and 10% (v/v) acetonitrile (pH 9.5) at 25 °C and 30 kV. Ink samples were extracted from black inkjet printouts with the use of dimethyl sulphoxide (DMSO).Differentiation of inks was based on the number of significant peaks at different wavelengths, the relative migration times and the characteristic UV–Vis spectra. The electropherograms of the inks extracted from paper showed patterns which in most cases were distinctly different from each other. The greatest diversity of electrophoretic profiles was revealed for documents printed by Hewlett-Packard inkjet technology. A database of electrophoretic separation results of inks has been constructed for further forensic use.

► Extract of various black inkjet printing inks were examined by MECC. ► A new analytical method was developed, optimized and validated. ► Inks were differentiated based on the peaks number, migration time, UV–Vis spectra. ► The greatest diversity of electropherograms was revealed for Hewlett-Packard inks. ► A database of electropherograms of analyzed inks has been constructed.