Analytical Sciences

Molybdenum Blue Spectrophotometry for Trace Arsenic in Ground Water Using a Soluble Membrane Filter and Calcium Carbonate Column

Takuya OKAZAKI, Wenjing WANG, Hideki KURAMITZ, Noriko HATA, and Shigeru TAGUCHI

Department of Environmental Biology and Chemistry, Graduate School of Science and Engineering for Research, University of Toyama, Gofuku 3190, Toyama 930-8555, Japan

An improved molybdenum blue spectrophotometry using a soluble membrane filter and CaCO₃-column was proposed for determining arsenic in drinking water supplied from ground water in the presence of phosphate. A 100 mL sample solution containing 0.5 – 10 μg arsenic was passed through a CaCO₃-column to remove phosphate, arsenate (As(V)). Arsenite (As(III)) which was not retained on the column was oxidized to As(V). As(V) was converted into a heteropolymolybdenum blue anion. The blue anion was collected on a membrane filter as an ion-associate with n-dodecyltrimethylammonium ion by filtration. The filter was dissolved in 2 mL of 2-methoxyethanol. The absorbance of the solution was measured at 810 nm against a reagent blank. Total inorganic arsenic was determined by reducing As(V) to As(III) before the column treatment. The RSDs for 10 μg L⁻¹ of As(III) and As(V) were 2.9%. Phosphate 0.2 mg L⁻¹ (as P) and iron 0.1 mg L⁻¹ did not interfere with the determination of 10 μg L⁻¹ arsenic. The proposed method was successfully applied to ground waters.

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