Determination of nickel by direct automatic potentiometric titration with EDTA and a chemically modified electrode based on a strong acid ion exchanger containing 4-(3,5-dichloro-2-pyridylazo)-1,3-diaminobenzene.
A chemically modified electrode (CME) was constructed and evaluated for use as an end-point indicator in the automatic titration of Ni(II) with EDTA. The CME consisted of a graphite paste prepared by mixing a strong acid ion exchanger containing 4-(3,5-dichloro-2-pyridylazo)-1,3-diaminobenzene and graphite powder-Nujol paste. This mixture showed high mechanical resistance in strongly acidic and alkaline solutions (6 M HCl-pH 12). The CME did not require any special conditioning prior to use. It could be used over long periods (5-6 months) of continuous work without renewing either the electroactive surface or paste. In buffered solutions (pH 3-4.5), automatic direct potentiometric titrations could be carried out over a wide interval of Ni(II) concentrations, ranging from 3 to 6000 ppm, with satisfactory accuracy and precision. For practical analysis, the electrode was applied to the determination of nickel in two certified composition alloys. Interferent ions were previously separated by applying an ion-exchange procedure.
González
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Departmento de Química Analítica "Dr. Carlos B. Marone", Universidad Nacional de San Luis, Chacabuco y Pedernera, CP 5700, San Luis, Argentina.
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Cortínez
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