Forensic Ink Analysis Using Thin-layer Chromatography Coupled With Colorimetry and Surface-enhanced Raman Spectroscopy - An Undergraduate Instrumental Analysis Experiment

This laboratory exercise provides hands-on learning for forensic ink analysis, and covers multiple techniques including silver nanoparticle synthesis, solvent extraction, colorimetry, thin-layer chromatography (TLC) as well as surface-enhanced Raman spectroscopy (SERS). Introducing forensic scenarios into the laboratory section of the traditional chemistry curriculum is an effective strategy to stimulate students’ overall interest in many sub-disciplines of chemistry. This experiment is our first attempt to infuse forensic topics into an upper-level undergraduate Instrumental Analysis course. The laboratory is designed to be a standalone experiment, which will enhance the students’ understanding of surface-enhanced spectroscopies especially SERS. During this 3-hour experiment, students will first prepare silver nanoparticles, extract ink from a questioned document, then separate the ink constituents along with six known ballpoint pen inks by TLC, and lastly, examine the colorful pen ink bands or streaks by SERS. This laboratory exercise could also be easily expanded to two 3-hour experiments with one emphasizing colorimetry/Beer’s Law and the other one focusing on TLC and Raman spectroscopy.