A rapid colorimetric method for measuring arsenic concentrations in groundwater

The arsenic content of groundwater consumed by millions of people in the developing world has become a major health concern. We report here an optimization of the colorimetric method of Johnson and Pilson (1972) to accurately measure As concentrations in the <0.03–5.3 (mu)mol L^-1 (<2–400 (mu)g L^-1) range in groundwater containing 2–30 (mu)mol L^-1 dissolved phosphate. The optimization includes increases in the concentrations of potassium iodate, ascorbic acid, antimonyl tartrate used for sample pre-treatment and color development that significantly lowered the detection limit and shortened the reaction time. Mean recovery obtained for a suite of groundwater samples from Bangladesh spiked with As in the 0.13–13 (mu)mol L^-1 (10–1000 (mu)g L^-1) range, the linear range of the method, was 97 (plus-minus) 5% (n = 10). The colorimetric method agrees within 5 (mu)g L^-1 for As concentrations up to 0.67 (mu)mol L^-1 (50 (mu)g L^-1) and within 4% in the 0.67–5.3 (mu)mol L^-1 (50–400 (mu)g L^-1) range with As analysis of the same Bangladesh groundwater samples by high-resolution inductively coupled-plasma mass spectrometry.