A validated reversed-phase thin-layer chromatography (RP-TLC)–densitometry method was developed and optimized for the determination of trimetazidine dihydrochloride (TMZ) and its potential impurities listed in the British Pharmacopoeia, namely, piperazinecarboxaldehyde (Y-145), trimethoxybenzyl alcohol (Y-235), and trimethoxybenzaldehyde (Y-234). Chromatographic separation was performed on aluminum plates pre-coated with silica gel 60 RP-18F using a mixture of acetonitrile–methanol–0.1% aqueous ortho-phosphoric acid pH 6.2 (4.5:4.5:1, V/V) as the developing system. Different factors affecting resolution were studied and optimized. Successful resolution was observed with significant difference in the RF
values of 0.21 ± 0.02, 0.35 ± 0.02, 0.5 ± 0.02, and 0.85± 0.02 for TMZ and its impurities, respectively. Densitometric measurement was done at 215 nm over the range of 0.05–10, 0.05–1.1, 0.05–1.2, and 0.04–1.0 µg per spot with lower limits of detection (LOD) and quantification (LOQ) of 20 and 50 ng per spot for TMZ, Y-145, and Y-235, respectively, and 15 and 40 ng per spot for Y-234 impurity. Good accuracy was obtained with mean percentage recoveries of 99.55 ± 1.06, 100.50 ± 1.16, 100.07 ± 1.24, and 99.41 ± 1.11 for TMZ and its impurities, respectively. The developed method was used to investigate the impurity profile of TMZ in drug substance and different products and it was validated as per the International Conference on Harmonisation (ICH) guidelines.