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 mumol L-1 (<2-400 mug L-1) range in groundwater containing 2-30 mumol 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 mumol L-1 (10-1000 mug L-1) range, the linear range of the method, was 97 +/- 5% (n = 10). The colorimetric method agrees within 5 mug L-1 for As concentrations up to 0.67 mumol L-1 (50 mug L-1) and within 4% in the 0.67-5.3 mumol L-1 (50-400 mug L-1) range with As analysis of the same Bangladesh groundwater samples by high-resolution inductively coupled-plasma mass spectrometry. (C) 2004 Elsevier B.V. All rights reserved.
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