Application of stability-indicating HPTLC method for quantitative determination of metadoxine in pharmaceutical dosage form

A sensitive, selective, precise and stability-indicating high-performance thin-layer chromatographic method for analysis of metadoxine both as a bulk drug and in formulations was developed and validated. The method employed TLC aluminium plates precoated with silica gel 60F-254 as the stationary phase. The solvent system consisted of acetone–chloroform–methanol–ammonia (7.0: 4.0: 3.0: 1.2, v/v/v/v). Densitometric analysis of metadoxine was carried out in the absorbance mode at 315 nm. This system was found to give compact spots for metadoxine (R_f value of 0.45 ± 0.02, for six replicates). Metadoxine was subjected to acid, alkali and neutral hydrolysis, oxidation, dry and wet heat treatment and photo and UV degradation. The drug undergoes degradation under all stress conditions. Also, the degraded products were well resolved from the pure drug with significantly different R_f values. The method was validated for linearity, precision, robustness, LOD, LOQ, specificity and accuracy. Linearity was found to be in the range of 100–1500 ng/spot with significantly high value of correlation coefficient r² = 0.9997 ± 1.02. The linear regression analysis data for the calibration plots showed good linear relationship with r² = 0.9999 ± 0.58 in the working concentration range of 200–700 ng/spot. The mean value of slope and intercept were 0.11 ± 0.04 and 18.73 ± 1.89, respectively. The limits of detection and quantitation were 50 and 100 ng/spot, respectively. Statistical analysis proves that the method is repeatable and specific for the estimation of the said drug. As the method could effectively separate the drug from its degradation products, it can be employed as a stability-indicating one. Moreover, the proposed HPTLC method was utilized to investigate the kinetics of acid and base degradation process. Arrhenius plot was constructed and activation energy was calculated respectively for acid and base degradation process.