Histidine as a New Coupling Agent for The Spectrophotometric Assay of Sulphadiazine – Application to Pharmaceutical Preparations

A simple and sensitive spectrophotometric method for the assay of sulphadiazine (SDA) in aqueous medium is described, the method is based on the formation of a yellow coloured azo dye from the diazotisation of SDA followed by a coupling reaction with histidine in alkaline medium of sodium hydroxide. The intensity of absorbance for the resulting yellow azo dye was measured at 423 nm and the azo dye was stable at least for 55 minutes. Beers law is obeyed in the concentration range of 10 240 g of SDA in a final volume of 25 ml, with a molar absorptivity of 1.75104 L.mol-1.cm-1, a relative error of +0.34 to +0.44% and a relative standard deviation of 0.34 to 0.87%, depending on the concentration level of SDA.
The method has been successfully applied for the assay of SDA in burn cream and in a veterinary injectable solution.