DISCRIMINATION STUDY BETWEEN BLUE BALLPOINT PEN INKS USING THIN LAYER CHROMATOGRAPHY AND UV-VIS SPECTROSCOPY TECHNIQUES.

Abstract

Scientific analysis of ink is often required as evidence in investigations involving questioned document examination (QDE) in a court of law relating to signatures and handwriting. Ink becomes important forensic evidence. Blue ballpoint pen inks commonly found in Thailand, were discriminated using two techniques of thin-layer chromatography (TLC) and UV-Vis spectroscopy. Results were assessed, calculated and compared in terms of discriminatory power (DP) of ink obtained as a common writing instrument. The ink was extracted from the documents using three different solvents as ethanol, acetone and dichloromethane by both techniques. The TLC method employed five different mobile phases to separate pigment and compounds in each sample, while UV-Vis spectroscopy recorded four types of data including wavelength of λmax, amplitude of λmax, shoulder and minor absorption peaks. Total of 435 possible pen-pairs were distinguished based on results of the chromatograms and UV-Vis spectra. The TLC method discriminated the ink samples into 12 groups by ethanol extraction. The highest classification power was the TLC method using ethanol as the solvent the mobile phase system 1 (n-butanol: ethanol: H2O in a ratio 50:15:10 by volume). The UV-Vis spectroscopy method recorded optimal DP at 77.24% for ethanol extraction. Results indicated that the TLC technique was a more effective tool for blue ballpoint pen ink analysis than UV-Vis spectroscopy technique. In the future, higher DP can be achieved. Multivariate statistical techniques applied for data interpretation may lead to the development of blue ballpoint pen ink test kits for real-time use at crime scenes.