Validated spectrophotometric methods for the evaluation of Oseltamivir counterfeit pharmaceutical capsules

Four rapid, reliable and economical spectrophotometric methods have been established for the quantitative determination of Oseltamivir phosphate (OST) without the interference of ascorbic acid (ASC) found in some of its counterfeit capsules. The first method involves the use of derivative spectrophotometry with the zero-crossing technique where OST was easily determined using its 1D (Δλ = 3) at 219 nm. The second method is based on a first-order derivative ratio spectrophotometry (1DD, Δλ = 5) where 218 nm was selected for its quantification, while the third method applies a more advanced spectrophotometric method based on the ratio difference spectrophotometry (RD) in which the difference in absorbance ratio was measured between 217 and 210 nm. In the fourth method, difference spectrophotometric method (ΔA) is applied by subtracting absorbance at 252 from that at 263 nm where the difference in absorbance was zero for ASC. The proposed methods were validated for linearity, accuracy, precision and selectivity. Synthetic mixtures of different proportions and commercial capsules were assayed by the proposed methods and the results revealed good accuracy and repeatability of the developed methods.