High-performance thin-layer chromatography‒spectrodensitometric determination of diltiazem hydrochloride and its commonly occurring degradation impurity

The present work encompassed the assay quantification of diltiazem hydrochloride and its degradation impurity F by high-performance thin-layer chromatography (HPTLC). HPTLC was performed with chloroform‒methanol‒formic acid (7.5:1.5:0.2, V/V) as the mobile phase and aluminum-backed thin layer chromatography (TLC) plates precoated with a 200 μm layer of silica gel 60 F₂₅₄ as the stationary phase. The densitometric chromatograms were performed at 254 nm, and the method was validated as recommended in the International Council for Harmonisation (ICH) guidelines. Statistical data from the analysis showed that the method is precise and highly sensitive. The correlation coefficient values of diltiazem hydrochloride and its impurity F were 0.9998 and 0.9975, respectively. The limit of detection was 76.81 ng/zone for diltiazem hydrochloride and 29.21 ng/zone for impurity F, while the limit of quantification was 232.77 ng/zone for diltiazem hydrochloride and 87.05 ng/zone for impurity F. The preciseness of the method was demonstrated and calculated as the % relative standard deviation for diltiazem hydrochloride and its impurity F. The mean recovery of the accuracy for diltiazem hydrochloride was between 98.23% and 100.29%, whereas for impurity F it was 100.02‒100.29%. The simplicity of the method proves its applicability for the quantification of impurity F during the synthesis of diltiazem hydrochloride.