Analytical Sciences

Spectrophotometric Determination of Arsenic in Water Samples Based on Micro Particle Formation of Ethyl Violet-Molybdoarsenate

Keisuke MORITA and Emiko KANEKO

Department of Materials Processing, Graduate School of Engineering, Tohoku University, Aoba 6-6-02, Sendai 980-8579, Japan

In this study, a simple and sensitive method for the determination of arsenic in water samples was developed. The method is based on the formation of micro particles of Ethyl Violet and molybdoarsenate, which gives an apparently homogeneous blue color to the solution. The absorption of the excess dye gradually decreases due to its conversion to a colorless carbinol species under strongly acidic conditions. Consequently, the sufficiently low reagent blank enables the spectrophotometric determination of arsenic with the detection limit of 4 µg l^-1. The coefficient of variation for the spectrophotometry at 50 µg l^-1 was 3.5% (n = 5). Furthermore, it is possible to detect concentrations as low as 10 µg l^-1 of arsenic visually. Our method will be useful as a simple, rapid, and cost-effective field test of arsenic, requiring no complex apparatus or skilled laboratory support.

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