An isocratic stability-indicating HPLC assay method was developed to quantitate ethacrynic acid in solution formulations. Utilizing the method, the main hydrolytic, and one of the oxidative degradation products could be separated. The structure of the separated degradation products was confirmed by negative ion-mode HPLC-MS. The hydrolytic results confirmed the previously reported sequence of the formation of the dimeric Michael adduct. One new oxidative metabolite has been identified. The validated analytical method can be used to quantitate ethacrynic acid in a solution formulation in the 0.5-500 µg/ml concentration range.


• forced degradation • hydrolytic degradation products • oxidative degradation products • michael addition reaction • stability-indicating HPLC method • HPLC-MS