Competent arsenicals: aqueous biphasic extractions and their application in nitrate/nitrite speciation

Abstract

The present article reports on the speciation of As(V) and As(III) using aqueous biphasic extraction based on a polyethylene glycol–salt system. For the detection of these inorganic arsenicals the salts of As(V) and As(III) are converted to their respective arsenomolybdenum blues having the formulae [As^VMo₄^V Mo₈^VIO₄₀]⁷⁻ and [As^IIIMo₄^V Mo₈^VIO₄₀]⁹⁻ and measured for their absorption spectra at 820 nm. These blue species are different in their extraction behaviour with the aqueous biphasic system. Once the blue solutions are formed they could further find application in the speciation of nitrite and nitrate in aqueous solution. A high molecular weight polymer, polyvinyl alcohol (PVA) was found to have a better efficiency to differentiate the nitrite and nitrate species. Kinetic studies show a proper decay rate of the As-blues with nitrite and no sensitivity for the nitrate species in PVA medium. This has been attributed to the structural property of PVA and its changes in the presence of the heteroplyacids. The results have been explained on the basis of changes in structural topology as revealed by the scanning electron microscope images.