The influence of the ammonium ion on the stability of ethacrynic acid in aqueous solution.

Investigations by reversed-phase HPLC into the stability of ethacrynic acid in buffered aqueous solutions containing either sodium or ammonium ions showed that the extent of degradation was influenced both by the species and concentration of the cation. A reported incompatibility between ethacrynic acid and the ammonium ion, attributed to the influence of the ammonium ion on an equilibrium existing between ethacrynic acid and one of its known degradation products, was shown to be due to the generation of an additional degradation product in ammonium-containing solutions only. This product was isolated and identified. Different pathways of degradation were shown to be operative in sodium- and ammonium-containing solutions. The addition of formaldehyde or a formaldehyde scavenger (hydroxyammonium chloride) was found to influence the rate of loss of ethacrynic acid, but the decomposition products provided no evidence for the existence of the reported equilibrium.