Determination of ppb level arsenic in well water

Coprecipitation of arsenic with iron(III) hydroxide is applied to the concentration of ppb-level arsenic in well water. Both of As(III) and As(V) are coprecipitated completely with iron(III) hydroxide in the range of pH 3.510.0. Water samples are acidified with hydrochloric acid to prevent the adsorption of arsenic on the wall of sampling bottles. Five milligrams of Fe(III) as chloride is added to 200 ml of sample and pH of the solution is adjusted to 710 with ammonia water. After standing the solution for 1 h the precipitate is filtered and dissolved in 25 ml of 4N hydrochloric acid and arsenic is determined with the atomic absorption method, using zinc powder tablets, potassium iodide and stannous chloride. The average recovery of As(III) and As(V) is 98% and the coefficients of variation are 5.5% and 4.9% for As(III) and As(V), respectively. Gutzeit method and photometric determination with molybdenum blue method after extraction using thionalide are also used after coprecipitation. More than 1.0 ppb of arsenic in well water can be determined with either the atomic absorption or the Gutzeit method after the coprecipitation. These methods can be successfully applied to the determination of arsenic in well water.