Preconcentration with Hydrous Lead(IV) Oxide for Spectrophotometric Determination- of Trace Amounts of Arsenic in Water Solutions

Abstract

The new preconcentration method of As(III) and As(V) with hydrous lead(IV) oxide (HLD)was developed. The adsorption curves of As(III) and As(V) on HLD in the pH range lower than 6 were very similar and the adsorption capacities of HLD for As(III) and As(V) at pH 3 were found to be about 1×10^-2 mol per mol of HLD. The adsorption mechanism of As(V) on HLD was the simple anionic adsorption type, while in the case of As(III), it was found that As(III) was oxidized to As(V) by HLD and then adsorbed on it. They could not be determined separately, however, HLD was considered to be useful to concentrate trace amounts of As(III) and As(V) in water sample solutions. Then the new recommended method for determination of arsenic in artificial river waters was developed as follows: The trace amounts of arsenic in a sample solution adjusted to a pH value of 2 was collected on HLD by shaking with it or passing through it loaded on a membrane filter. The HLD was filtrated off, and dissolved with EDTA solution. After Pb(II), produced from HLD, was removed from the solution with the Dowex 50 W resin, arsenic was determined by spectrophotometry using ammonium molybdate-Marachite- Green reagent. As the results, 0.1-10pg of arsenic was determined with good recovery. The presence of diverse ions added in the artificial river water samples had no significant influence on the preconcentration and determination of arsenic. The detection limit of arsenic in the artificial river water samples was determined to be 0.05 ppb.