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Abstract
A simple and selective HPLC-DAD method was developed for the simultaneous determination of nifuroxazide and drotaverine hydrochloride in their combined pharmaceutical formulation. Effective chromatographic separation was achieved using a Zorbax SB-C18 (4.6 × 250 mm, 5 µm) column with gradient elution of the mobile phase composed of 0.05 M phosphoric acid and methanol. The multiple wavelength detector was set at 245, 285, and 370 nm. The retention times for nifuroxazide and drotaverine were approximately 7.5 and 10.4 min, respectively. The reliability and analytical performance of the proposed HPLC procedure were statistically validated with respect to linearity, ranges, precision, accuracy, selectivity, robustness, detection, and quantification limits. Calibration curves were linear in the range 1–40 g/mL for both nifuroxazide and drotaverine with correlation coefficients >0.9993. Both drugs were subjected to stress conditions of hydrolysis, oxidation, and photo-degradation. The proposed method proved to be stability-indicating by the resolution of the two analytes from the forced-degradation products. The validated HPLC method was applied to the analysis of this pharmaceutical mixture in capsules where the two analytes were successfully quantified with recoveries not less than 98.5%, and no interfering peaks were encountered from the inactive ingredients. Moreover, the proposed method was utilized to investigate the kinetics of the acidic and basic hydrolysis processes. The corresponding pseudo-first order rate constants and half-lives were calculated. Finally, the proposed method made use of DAD as a tool for peak identity and purity confirmation.
Notes
t R = Retention time (min); N = Number of theoretical plates; k′ = Capacity factor; α = Selectivity between NX and DV peaks; R s = Resolution between NX and DV peaks; T f = Tailing factor.
LOD = Limit of detection; LOQ = Limit of quantification; Sa = Standard deviation of intercept; Sb = Standard deviation of slope; Sy/x = Standard deviation of residuals; F = Variance ratio, equals the mean of squares due to regression divided by the mean of squares about regression (due to residuals).
a Mean ± standard deviation for three determinations.
RSD (%) = Percentage relative standard deviation; Er (%) = Percentage relative error.
a Mean ± standard deviation for three determinations.
RSD (%) = Percentage relative standard deviation; Er (%) = Percentage relative error.
a Mean ± standard deviation for five determinations.
RSD (%) = Percentage relative standard deviation.
Theoretical values for t and F at P = 0.05 are 2.31 and 6.39, respectively.