Direct and indirect spectrophotometric determination of some selected antibiotics using potassium permanganate

Two spectrophotometric methods were developed for the quantitative determination of Cefoperazone (CFP) and Amoxicillin (AMX) in pure forms as well as their active pharmaceutical ingredients (API). The methods are based on a redox reaction between the selected drugs and KMnO4 in alkaline or acid media. Direct spectrophotometry (method A) involves treating the aqueous solution of the selected drugs with KMnO4 in alkaline medium and measuring the bluish-green product at 610 nm. In indirect spectrophotometry (method B), the drug solutions were treated with a fixed concentration of KMnO4 in acidic medium followed by the determination of the unreacted oxidant by measuring the decrease in absorbance of methylene blue at 665 nm. The different experimental parameters affecting the development and stability of the color were carefully studied and optimized. Beer's law is obeyed over 2.0-40 (method A) and 0.8-7.2 mu g/mL (method B). The molar absorptivity, Sandell sensitivity, detection and quantification limits were also calculated. The intra- and inter-day relative standard deviation (RSD) values demonstrated the validity of the two methods for the drugs in pure form and as the API. Statistical comparison of the results with a well-established official method showed excellent agreement and proved that there is no significant difference in the accuracy and precision.