1987 Volume 36 Issue 3 Pages 189-193
A simple and rapid method for the determination of trace amounts of arsenate, arsenite and phosphate in sample water was proposed. Molybdophosphateand molybdoarsenate-Marachite Green aggregates formed by Mo-MG reagent(mixed solution of ammonium molybdate and Malachite Green) were selectively collected on a nitorocellulose membrane filter (3 μm pore size), and the aggregates were dissolved in a small volume of methylcellosolve together with the membrane filter. The absorbance (λ : 627 nm), denoted as A {P+As(V)}, was proportional to the sum of the concentrations of phosphoric and arsenic aggregates with molar absorptivity of 2.6×105 M-1 cm-1. Thiosulfate was added to the second portion of the sample water, as a reducing agent for arsenate to arsenite, and the absorbance of the solution, A(P), was measured in the same way as described above. A(P) corresponds to the concentration of phosphate alone. Iodate, an oxidizing agent for arsenite to arsenate, was added to the third portion of the sample water, and the absorbance of the solution, A{P+As(V)+As(III)}, was measured. The difference between A{P+As(V)} and A(P), and that between A{P+As(V) +As(III)} and A{P+As(V)} lead to the arsenate and arsenite concentrations, respectively. The present method makes it possible to determine arsenate, arsenite and phosphate as low as 0.3 ppb arsenic(III, V) and phosphorus.
