Automatic determination of arsenate in drinking water by flow analysis with dual membrane-based separation.

The sequential application of a polymer inclusion membrane (PIM), composed of poly(vinylidenefluoride-co-hexafluoropropylene) and the anionic extractant Aliquat 336, and a microporous polytetrafluoroethylene (PTFE) gas-permeable membrane was utilized for the first time to develop a flow analysis (FA) system, for the automatic determination of trace levels of arsenate (As(V)) in drinking water as arsine. The system incorporated a flow-through extraction cell for separation and preconcentration of arsenate and a gas-diffusion cell for the separation of arsine prior to its spectrophotometric determination based on the discoloration of a potassium permanganate solution. Under optimal conditions the FA system is characterized by a limit of detection of 3.0 μg L-1 As(V) and repeatability of 1.8% (n = 5, 25 μg L-1 As(V)) and 2.8% (n = 5, 50 μg L-1 As(V)). The newly developed FA method was successfully applied to the determination of arsenate in drinking water samples in the μg L-1 concentration range.