Separation of Blue Ballpoint Pen Inks- A Comparison of Solvent Systems on Thin Layer Chromatography Techniques
Keywords:Forensic, Ballpoint pen inks, Thin-layer chromatography, Ink analysis
This article is chromatographic analysis of inks for forensic science. Thin layer chromatographic technique (TLC) is often used in separation of writing inks because it is rapid and requires no sophisticated instrumentation. The repeatability and reproducibility of TLC analyses of inks depend on several factors. However, the critical importance is the use of solvent for the extraction process and for mobile phase. The purpose of the present study is to compare the effectiveness of blue ballpoint pen ink separation by TLC
between different solvent extraction and variant mobile phase systems. Thirty blue ballpoint pens commonly used in Thailand were extracted from document then three solvents (ethanol, acetone or dichloromethane) and five solvent systems as mobile phase were used to separate pigment compounds in each sample. The Rf values were calculated for discrimination analysis of all blue pens via two-way ANOVA. The results showed that the most important factor affecting ink classification was solvent extraction. The ethanol was the best solvent for extraction and the optimal mobile phase was n-butanol: ethanol: water (50:15:10 v/v/v) having statistically
significant level of 0.05. This mobile phase system could be used to classify all 30 inks into 12 different groups with the discrimination power (DP) of 89.20%. In the future, the qualitative data from TLC plates will more reliable by multivariate statistical techniques can also be applied on effectively interpretation.
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