Stability-indicating high-performance thin-layer chromatographic determination of zidovudine as the bulk drug and in pharmaceutical dosage forms

A sensitive, selective, precise, and stability-indicating high-performance thin-layer chromatographic method has been established and validated for analysis of zidovudine both as the bulk drug and in formulations. The method employs aluminum-backed silica gel 60F(254) HPTLC plates with toluene-carbon tetrachloride-methanol-acetone, 3.5 + 3.5 + 2.0 + 1.0 (v/v), as mobile phase. This system was found to give compact spots (R-F 0.41 +/- 0.02) for zidovudine. Densitometric analysis of zidovudine was performed in absorbance mode at lambda = 270 nm. Response was linearly dependent on amount of zidovudine in the range 100-6000 ng per spot with a significantly high correlation coefficient (r(2) = 0.998 +/- 0.53). Linear regression analysis data for the calibration plots showed there was a good linear relationship with r(2) = 0.998 +/- 0.0003 in the working concentration range 100 to 1000 ng per spot. The mean values of the slope and intercept were 0.063 +/- 0.004 and 39.61 +/- 1.09, respectively. The method was validated for precision, robustness, and recovery. The limits of detection and quantitation were, respectively, 20 and 40 ng per spot. Statistical analysis proved the method was repeatable and selective for estimation of the drug. Zidovudine was subjected to acid and alkaline hydrolysis, to oxidation, to dry and wet heat treatment, and to photodegradation; it was found to undergo degradation under all these conditions except dry heat treatment. The degradation products were well separated from the pure drug with significantly different R-F values. Because the method can effectively separate the drug from its degradation products, it can be employed for stability-indicating analysis. The proposed HPTLC method was used to investigate the kinetics of acid degradation. An Arrhenius plot was constructed and the activation energy was calculated.