Extraction of colour inkjet printing inks from printouts for forensic purpose

The ability to differentiate between inkjet printing inks is of great interest in document examination. The aim of this work was to develop a procedure for effective ink extraction so that the ink could be reliably analyzed by capillary electrophoresis. Conditions such as type and composition of extracting mixtures, as well as duration of extraction and sonication procedures were taken into consideration. A set of different agents was used to extract inks of inkjet printers produced by Hewlett-Packard, Canon, Brother, Epson and Lexmark. Extraction efficiency was examined visually and then by means of UV/Vis spectrometry. It was ascertained that the most promising extracting agents are mixtures of borate buffer with SDS and with acetonitrile, or alternatively with methanol, which are both suitable background electrolytes for further CE analysis. However, in some exceptional cases, highly efficient extraction was achieved by a mixture of DMF, DMSO, EtOH and MEE with water.