Use of ethylenediaminetetraacetic acid as a pH buffer to prevent copper(II) interference by complexation in the cathodic stripping voltammetric determination of reducible organic compounds at a hanging mercury drop electrode: determination of sulfasalazine in the presence of sulfadimidine

Abstract

Non-reducible organic compounds that can be accumulated at a hanging mercury drop electrode as copper(I) complexes or salts, and can then be determined indirectly by reduction of the copper(I), may interfere in the determination of reducible compounds that adsorb on the electrode and are determined directly by cathodic stripping voltammetry. This would occur if there were appreciable amounts of copper(II) in the sample or in the de-ionized water supply. The prevention of this interference by the use of ethylenediaminetetraacetic acid as the pH buffer is illustrated here in determining sulfasalazine, a sulfonamide drug which has a reducible azo group, in the presence of significantly larger amounts of sulfadimidine (which is not reducible) and copper ion. In this type of application the EDTA serves a dual purpose as the pH buffer and as a complexant to mask interfering cations, such as copper(II).