Hypophosphite ReductionIodometric Titration of Arsenic in Ore Samples

The ore sample (0.5 g) is dissolved in 20 mL of HNO3HCl (3+1) mixed acid and fumed with 5 mL of H2SO4. After cooling, the salts are dissolved with 70 mL of warm HCl (1+1) solution. Arsenic (Ⅲ or Ⅴ) in the solution is reduced to elementary state by adding sodium hypophosphite with 1 to 2 g in excess using 0.1 g of CuSO4 as catalyst. After filtration and washing, the precipitate of elementary arsenic together with the filter paper is removed to the beaker and an excess and definite amount of iodine standard solution is added to dissolve the As° completely, and the excess amount of iodine is titrated with Na2S2O3 standard solution in a medium of 20 g·L-1 NaHCO3 solution. Based on the volume of the 2 standard solutions consumed in dissolution of As° and titration of excess of iodine, content of arsenic in the sample is calculated. Three standard samples were analyzed by the proposed method, and contents of arsenic found were in consistency with the certified values, with values of RSD′s (n=5) ranged from 1.5% to 2.1%.