Application of High Performance Thin Layer Chromatography in Examination of Magenta Coloured Printed Matter

Abstract

The technique of High Performance Thin Layer Chromatography was utilized to separate the components of magenta colour inkjet printer ink. An attempt has been done to develop a protocol to examine and opine on the issue of identification of printer from which a document was printed. I. Introduction From the moment that a writing ink is applied to paper material, the chemical composition of ink begins to undergo changes. Various physical and chemical processes occur such as the evaporation of solvent; spreading of ink, paper corrosion etc. Modern inks are the mixtures of various components to provide different physical and chemical properties to ink such as colorants (dyes or pigments), Solvent, surfactants, humectants, biocides, fungicides, buffering agents and resins. Additionally, other organics may be used to control corrosion or improve solubility of the dyes and pigments. Current methods for the examination, identification and comparison of inks on paper include a wide variety of techniques, ranging from optical examination, microscopic and spectroscopic studies of the ink. Some techniques require damaging the sample by mechanical or chemical removal of ink from paper. Various forms of chromatography such as column, paper, thin layer, gas and liquid chromatography have gained prominence from past several decades to separate the components of inks. Thin Layer Chromatography involves a stationary phase through which a solvent system migrates across the plate by capillary action, separating the ink components. The process involves carrying the components of ink by a mobile phase through a stationary phase. The separation of dyes, colourless organic components as well as non-volatile components occurs due to their different migration rates. The several samples can be examined on the same TLC plate whereas the TLC densitometry is used in absorption or reflection mode in visible/UV254/UV366 mode to determine the relative concentrations of the dyes present and other components. In the present study the fast, reliable, and economical technique of HPTLC was used for direct comparison and identification of ink. The technique involves use of very small sample and is sensitive because of the intense colour of dye components in the visible region, absorption in UV region and fluorescence.