Flow injection spectrophotometric determination of As(III) and As(V) using molybdate reagent with solid phase extraction in-valve column

Abstract

Flow injection (FI) spectrophotometry for speciation of As(III) and As(V) has been investigated. As(III) in a mixture of AsO₂^- and ASO₄^3- merging with IO^3- will convert into As(V). The total ASO₄^3- forms heteropoly acids with molybdate reagent. Mo(VI) is subsequently reduced to Mo(V). The compound in the stream flows into an in-valve microcolumn packing with C₁₈ resin. The sorbed As-complex is eluted and continuously monitored by an LED colorimeter. The signal corresponds to the sum of AsO^2- and ASO₄^3-. A signal obtained without merging with IO^3- is that of the ASO₄^3-alone in the mixture. Optimization for the conditions has been investigated. Single standard As(V) calibration is possible. Application to a sample free from phosphate such as water leachates of zinc ores has been demonstrated.