Analytical Sciences

On-line Electrochemical Oxidation of Cr(III) for the Determination of Total Cr by Flow Injection-Solid Phase Spectrophotometry

Shiro MATSUOKA,* Yu NAKATSU,** Kô TAKEHARA,** Sulistyo SAPUTRO,*** and Kazuhisa YOSHIMURA**

*Department of Environmental Science, Faculty of Science, Niigata University, Ikarashi, Niigata 950-2181, Japan
**Department of Chemistry, Faculty of Sciences, Kyushu University, Ropponmatsu, Chuo, Fukuoka 810-8560, Japan
***Department of Mathematics and Natural Science Education, Faculty of Teacher Training and Education Sciences, Sebelas Maret University, Jl. Ir. Sutami No. 36A, Kentingan, Surakarta-57126, Indonesia

A novel on-line oxidation method of ultra-trace Cr(III) dissolved in natural water has been developed using a flow electrolysis cell. This method was successfully applied to the determination of the total Cr concentration by flow injection-solid phase spectrophotometry using diphenylcarbazide as a coloring agent. With the applied potential of 1.35 V (vs. Ag/AgCl) and the flow rate of 0.80 cm³ min^-1, Cr(III) was quantitatively oxidized to Cr(VI) at room temperature. The total Cr concentration of sub-µg dm^-3 in 3 - 4 samples could be determined within 1 h using an aqueous sample volume of 7.1 cm³. The analytical values of the total Cr concentration in natural water were in good agreement with those obtained by ICP-MS. The detection limit of the proposed method was 0.014 µg dm^-3 (3σ, n = 7). This method could be applied to the specific determination of Cr(III) and Cr(VI) in river water samples.

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