FIXED SIZED SIMPLEX OPTIMIZATION OF SPECTROPHOTOMETRIC METHOD FOR THE QUANTITATIVE DETERMINATION OF DICLOFENAC IN PHARMACEUTICAL PREPARATIONS

A simple method was developed for spectrophotometric determination of diclofenac sodium in pharmaceutical preparations using potassium permanganate to form a brown complex in the presence of slightly acidic sulphuric acid media. This complex was monitored at 455nm wavelength. Simplex optimization procedure was used to optimize the factor levels, and the method was validated and successfully applied to the assay of 11 brands of the pharmaceutically-formulated analyte. Calibration curve was linear within the range of 5µg/L – 35µg/L concentrations (r2= 0.998). The method was precise as shown by the intra-day (repeatability) and inter-day (reproducibility) indices of precision, 0.56% and 0.45% respectively. The limit of detection was estimated to be 0.158mg/L, while the limit of quantitation was 0.525mg/L. Recoveries were calculated as 89.78% - 104%. Statistical paired t–test showed that there was no significant difference on comparing the developed method with the official method in British Pharmacopeia. However, Chauvenet’s criterion applied to the data revealed that “SortenForte” was an outlier and therefore a possible counterfeit or substandard formulation. The newly developed method compared favorably, and can effectively serve as an alternative, to the official method for routine determination of the analyte in pharmaceutical preparations.