Analytical Sciences

A Kinetic Method for the Determination of Copper(II) by Its Catalytic Effect on the Oxidation of 3-Methyl-2-benzothiazolinone Hydrazone with Hydrogen Peroxide: A Mechanistic Study

Takashi TOMIYASU, Satoshi AIKOU, Katsuro ANAZAWA, and Hayao SAKAMOTO

Department of Earth and Environmental Sciences, Faculty of Science, Kagoshima University, Korimoto, Kagoshima 890-0065, Japan

A catalytic spectrophotometric method for the determination of traces of copper(II) is proposed. 3-Methyl-2-benzothiazolinone hydrazone (MBTH) is oxidized by hydrogen peroxide to form a yellowish-brown compound. The reaction is accelerated by trace amounts of copper(II), and can be followed by measuring the increase in the absorbance at 390 nm. Since the absorbance at 40 min from the reaction start increases with an increase in the copper(II) concentration, the absorbance value is used as a parameter for copper(II) determination. Under the optimum experimental conditions (8.4 × 10^-3 mol dm^-3 MBTH, 0.7 mol dm^-3 hydrogen peroxide, pH 5.2, 35°C), copper(II) can be determined in the range 0 - 50 µg dm^-3. The relative standard deviations are 6.9, 3.5, 2.7% for 2, 20 and 40 µg dm^-3, respectively. The detection limit of this method (3 σ) is 0.27 µg dm^-3. It was successfully applied to a determination of copper(II) in river water, tap water and ground-water samples. According to the results of a kinetic study, a mechanism is proposed which leads to the following rate equation: R_0cat = kK₁K₂[MBTH][H₂O₂][Cu(II)]₀/{(1 + K₂[H₂O₂])[H⁺]}.

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