Detection and Discrimination (On the Basis of Brand) of Different Permanent Marker Ink Brands Using ¹H NMR Spectroscopy

Permanent marker inks are frequently encountered as evidentiary material in forensic document examination, including cases of forgery, alteration, anonymous writing, and product counterfeiting. Conventional techniques such as thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC), Fourier-transform infrared spectroscopy (FTIR), and Raman spectroscopy have long dominated ink analysis, but each carries limitations in terms of sample consumption, resolution of closely related dye/solvent formulations, or reproducibility across analysts. This study explores the application of proton nuclear magnetic resonance (¹H NMR) spectroscopy as a rapid, non-destructive (at the extraction stage), and highly reproducible technique for the detection and brand-level discrimination of permanent marker inks. Ink samples were extracted from writings produced by ten commercially available permanent marker brands using a standardized solvent-extraction protocol and analyzed on a 400 MHz NMR spectrometer. Spectral data were interpreted with reference to characteristic chemical shift regions corresponding to solvent systems (xylene, toluene, alcohols), resin binders, and dye/pigment-associated aromatic protons. Chemometric treatment of the spectral data, including principal component analysis (PCA) and hierarchical cluster analysis (HCA), was performed to statistically validate brand-wise discrimination. The results demonstrate that ¹H NMR spectroscopy can reliably differentiate permanent marker ink brands based on distinct spectral fingerprints arising from formulation-specific solvent ratios and additive profiles, establishing its utility as a complementary and, in some respects, superior analytical tool in forensic ink examination.