4-(3,5-Dichloro-2-pyridylazo)-1-3-diaminobenzene-graphite paste electrode for end-point detection in the automatic potentiometric titration of zinc(II) with EDTA

A simple and sensitive potentiometric sensor for end-point detection in the automatic titration of Zn(II) with EDTA was prepared and studied. The sensor was based on a conventional carbon paste which was mixed during preparation with 4-(3,5-dichloro-2-pyridil-azo)-1,3-diaminobenzene (3,5-Cl2PADAB). pH effects, buffer concentration, reagent content into carbon paste and the presence of foreign salts on the electrode response were studied. Titration curves with sharp end-point breaks were obtained in Zn(II) concentration range from 0.5 to 6550 ppm. The electrode was easily made and with very inexpensive materials. A titrimetric method for the determination of zinc in insulin by automatic potentiometric end-point detection is described. It was applied to the determination of the metal in two commercial pharmaceutical preparations. The results were in good agreement with those obtained by the U.S. Pharmacopeia standard method.