Comprehensive Survey Of The Thin-layer Chromatography And Hplc Pen Ink

With the development of computer and internet, electronic communication, electronic signatures and a whole array of electronic business transactions become more and more popular, but the ink- based document remains widely used and trusted for any business and legal documents. So the problem of questioned document remains a very important problem in forensic science. In this article we researched on the classification of 90 kinds of black signing-pens and 94 kinds of blue signing-pens, which manufactured by the different domestic and foreign factories. In this project, various types of chromatography for the identification of inks were investigated, including thin-layer chromatography (TLC) and high performance liquid chromatography (HPLC). First, We summarized the main composition of inks including dyestuff, solvent, resin and resistance to oxidation, heat, light, water, etc and then recapitulated the discrimination of questioned documents by chromatography including TLC and HPLC .Secondly, we systematical analyzed on the signing-pens with thin-layer chromatography (TLC) and high performance liquid chromatography (HPLC).TLC is a very popular technique due to the ease of use, speed and cost effectiveness. The retardation factor, R_f value of a compound of ink is dependant on the absorbent and mobile phase, and the numbers and colours of spots can be used to identify the difference among the inks. In the condition of this experiment, the black signing-pens are separated into 9 kinds, and the blue signing-pens are separated into 11 kinds. The resolution of TLC is limited and can often prove incapable of differentiation between different batches of ink with the same general composition. HPLC can improve the ability to distinguish between inks owing to their greater sensitivity and resolving power. We explored an HPLC method to identify these signing-pens. The method involved the use of a Purospher STAR column, with TBA(0.004g/mL,pH6.5) and NH₄HCO₃(10mmol/L,pH8.0) in mobile phase which is suitable for black and blue signing-pens separately, and a diode array multiwavelength detector scanning from 400-700 nm. HPLC was capable of the detection of subtle batch differences, not differentiated by TLC. Finally, on the base of the TLC results, black signing-pens and blue signing-pens were classified again.