Spectrophotometric determination of inorganic arsenic (III) and (V) in water using the molybdenum blue method

Arsenic surface water and groundwater pollution is a reported issue in many developing countries, thus it is of great concern to quantify this species by using economic techniques easy to handle. In this work, a spectrophotometric method for the quantification and speciation of arsenic in the presence of phosphorous in water was developed. It is based on the generation of a colored complex (heteropolyacid) in acid media, by arsenate reaction with molybdate. For total arsenic determination, potassium iodate was used for the quantitative oxidation of trivalent arsenic. Trivalent arsenic was determined from the difference between the total arsenic quantified and the arsenate. Phosphorous (V) was quantified by using L-cysteine, by the selective reduction of pentavalent arsenic. The developed method allowed to quantify arsenic at ultra-trace levels (mu g/L), presenting the following figures of merit of the analysis: Detection limit 6 mu g/ L, quantification limit 18 mu g/L, linearity from 18 to 1600 mu g/L; 96.9 % of recovery and 1.24 % of precision. The results were comparable to those obtained by atomic absorption spectrometry with graphite furnace.