Coprecipitation concentration of arsenic with iron(III) hydroxide in the presence of triton X-100.

Iron(III) hydroxide precipitate, which is a quantitative precipitant for arsenic in water, was easily separated by pipetting out the supernatant solution and filtration after aging in the presence of triton X-100. Arsenic(0.2-10 μg) in water(1 1) was successfully concentrated with this method. Ten mg of iron(III) was added to 1 1 of water samples, and the pH was adjusted to 7-9 to precipitate iron(III) hydroxide. After the addition of 2 ml of 2% triton X-100, the solution containing precipitate was warmed in a hot water bath for 40 min to form large flocks which settle down to the bottom. After standing overnight, about 600 ml of the supernatant solution was removed. The precipitate was filtered through No.5A filter paper and dissolved in 30 ml of (1+3) hydrochloric acid. The content of arsenic was determined with Ag-DDTC spectrophotometric method. The recoveries of iron, arsenic(III) and arsenic(V) were 99.6, 96.5 and 96.5%, respectively.