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The potential of capillary electrophoresis coupled to mass spectrometry with electrospray ion source and time of flight analyser (CE-ESI-TOF-MS) in the analysis of inkjet inks was investigated. The developed and validated method allowed reliable and repeatable analysis of black inkjet inks extracted from printouts. Over a dozen inkjet printouts printed on various printer models from different manufacturers were analysed under selected conditions to determine the variation of chemical composition of inks between different brands and types. It was ascertained that the developed method is capable of revealing qualitative differences between ink samples. For most of the investigated inks, the studies showed the presence of a characteristic mass spectrum originating from the surfactant or polymer. The mass distribution of the additive is distinctive for some inkjet ink producers, and allows for group identification of inks. The results showed the strength of the CE-ESI-TOF-MS method as an effective technique for forensic purposes, requiring a small amount of inkjet ink samples and giving analytical information that is useful in the identification of compounds.

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 (60/50cm total/effective length, 75μm i.d.) with a background electrolyte composed of 40mM sodium borate, 20mM SDS and 10% (v/v) acetonitrile (pH 9.5) at 25°C and 30kV. 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.

A combination of MEKC with a--highly sensitive but not commonly used--LIF detector was tested regarding the possibility of differentiation of red inks. The separation process was conducted in a fused silica capillary (id 50 μm, 60/50 cm total/effective length) in BGE consisting of 40 mM sodium borate, 20 mM SDS and 10% v/v ACN with 30 kV applied. The optimized temperature of storage and capillary was 10 and 25°C, respectively. The samples were prepared using 20 dots (ø 0.5 mm), extracted in 35 μL BGE and diluted with 30 μL of water. The proposed method showed excellent repeatability and reproducibility (RSD (tm ) < 0.8 and < 2.5%, respectively). It was applied to group identification and differentiation of different brands, models, and batches of red printing, stamp, and pen inks. It was demonstrated that differentiation can be performed effectively on the basis of migration times and ratios of peak areas. The high efficiency of the developed method was indicated by discriminating power ranging from 87.3 to 98.8%, for stamp and pen inks, respectively. The results showed that the proposed procedure can be valuable for an objective examination of the red parts of questioned documents.