Determination of diclofenac sodium and related compounds in raw materials and formulations

A liquid chromatographic method has been developed for determination of drug and related compounds in diclofenac sodium raw material, slow-release, and enteric coated tablets. The method specifies a 5 microns octadecylsilane bonded phase column, a mobile phase of tetrahydrofuran-acetonitrile-buffer, pH 5 (1 + 4 + 8.3), and detection at 229 nm. The method resolves 10 known related compounds with limits of quantitation of 0.2% or less. Seventeen drug raw material samples were evaluated. Total impurity levels ranged from 0.1 to 0.9%. The method has also been used for determination of drug content in raw materials and formulations. Mean assay levels in drug raw materials ranged between 98.3% and 101.8%.