Spectrophotometric determination of diclofenac sodium in tablets

Simple spectrophotometric methods are described for the determination of diclofenac. In the first method diclofenac reduces iron(III) to iron(II) when heated in aqueous solution. The ferrous ions produced react with 2,2'-bipyridine to form a complex having a maximum absorbance at 520 nm. The reaction obeys Beer's Law for concentrations of 10-80 micrograms ml-1. This method can be applied to the determination of diclofenac in tablets. In the second method, diclofenac is treated with Methylene Blue in the presence of phosphate buffer (pH 6.8) and the complex is extracted with chloroform. The complex has a maximum absorbance at 640 nm and the graph of absorbance against concentration is linear in the range 5-40 micrograms ml-1. This method can be applied to the determination of diclofenac in tablets that also contain paracetamol.