Spectrophotometric Determination of Sulphamethazine by the Diazotisation-Coupling Method with m-Aminophenol as the Coupling Agent-Application to Pharamaceutical

A spectrophotometric method for the trace determination of sulphamethazine has been worked out. It is based on the reaction of sulphamethazine with sodium nitrite in acidic medium to form the corresponding diazonium salt. After removal of excess nitrite with sulphamic acid, the diazotised sulphamethazine is coupled with m-aminophenol fo form an intensely-yellow coloured, water-soluble and stable azo dye which shows maximum absorption at 457 nm. The plot of absorbance versus determinand concentration shows that Beer’s law is obeyed over the concentration range 5-150 g sulphamethazine/25 ml final volume, i.e., 0.2-6 ppm with a molar absorptivity of 4.8X104
l.mol-1.cm-1. The method has been applied to the assay of the drug in a tablet.