title: Arsenite oxidation and arsenate determination by the molybdene blue method.
abstract: Based on the similarity in properties of arsenate and phosphate, the colorimetric method using the molybdene blue complex was tested in order to determine low As(V) concentration in waters. The influence of complex formation time, daylight, temperature and competitive anions (silicate and sulphate) upon complex formation was determined. Optimal complex formation was reached in 1 h at 20+/-1 degrees C and was slightly favoured when developed in daylight. The formation rate declined with decreasing reaction temperature and no influence of any of the competitive anions tested (at concentrations usually found in natural waters of granitic areas) was noted. The detection limit of this method was 20 mug As(V) l(-1). This simple, fast and sensitive arsenic determination method is suitable for field analysis, especially for waters containing low levels of phosphate and organic matter. Through arsenate determination, this colorimetric method allowed the arsenite oxidation efficiency of five common industrial oxidants to be compared. H(2)O(2) and MnO(2(s)) were not considered as effective oxidants as a high excess was necessary to ensure As(III) oxidation. NaOCl and KMnO(4) were promising oxidants as they allowed complete arsenite oxidation with a small excess for NaOCl or even less than the electron stoichiometric ratio in the case of KMnO(4). FeCl(3) was the most effective oxidant among the reagents tested here.
authors.affiliation: Laboratoire des Sciences de l'Eau et de l'Environnement, Faculté des Sciences, 123 avenue Albert Thomas, F 87 060 Limoges, France.
authors.forename: Véronique
authors.initials: V
authors.lastname: Lenoble
authors.forename: Véronique
authors.initials: V
authors.lastname: Deluchat
authors.forename: Bernard
authors.initials: B
authors.lastname: Serpaud
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Bollinger