DEVELOPMENT OF A SPECTROPHOTOMETRIC METHOD FOR DETERMINATION OF CEPHALEXIN USING SODIUM 1, 2-NAPHTHOQUINONE-4-SULFONATE AND CENTRAL COMPOSITE DESIGN

A spectrophotometric method for determination of cephalexin is proposed. This method is based on the formation of a colored compound in the reaction of cephalexin with sodium 1,2-naphthoquinone-4-sulfonate (NQS). The effects of various experimental parameters in this reaction were investigated and optimized using central composite design (CCD). Twelve experiments with two factors and five levels for each factor were designed. These factors include concentration of NQS and pH. A full-quadratic polynomial equation between the absorbance as the response and the studied parameters was established. After removing the non-significant terms from the model, response surface method was used to obtain the optimum conditions. The optimum values of factors were 20.0×10^-4 M for concentration of NQS and 9.6 for pH. The maximum absorption wavelength and the value of absorptivity of the colored product were 475 nm and 1.79×10³ L mol⁻¹ cm⁻¹, respectively. The absorbance of the reaction product obeys Beer’s law in the range 1.5-34.0 mgL^-1. The detection limit of the method was 0.43 mgL^-1. This method is rapid and simple, and can be used for the determination of cephalexin in formulations (capsules and injections). Recovery of 98.8% was obtained in application of the method to the real samples.