Ion-selective electrodes in titrations involving azo-coupling reactions

An organic cation-selective indicator electrode based on a PVC membrane plasticized with 2-nitrophenyl 2-ethylhexyl ether can be used in potentiometric titrations of aromatic hydroxy compounds, amines, and compounds containing active methylene groups, with 4-methyl-, 4-bromo-, or 4-nitro-benzenediazonium chloride solutions as titrants. Useful results were obtained in determinations of 16 passive components, including 2-naphthol, some 2-naphthol sulfonic acids, 8-quinolinol and its 5-sulfonic acid, ammo-1-naphthol-3-sulfonic acids, 1-naphthylamine sulfonic acids, resorcinol, 2,4-toluylenediamine, two acetanilide derivatives, and two substituted sulfophenyl pyrazolone derivatives. 4-Bromobenzenediazonium chloride proved to be the best titrant of the diazonium salts tested.