Potentiometric sensor for L-ascorbic acid based on EVA membrane doped withcopper(II)

The development of a new potentiometric sensor for L-ascorbic acid based on the redox properties of copper(II) ions incorporated in a EVA membrane was carried out. The poly(ethylene-co-vinyl acetate) matrix (EVA 40 % wt.) was doped with CU2+ ions and dispersed on the surface of a graphite/epoxy elec trode. The electrode displayed a Nernstian response (slope between 55 and 6 0 mV/decade), in the ascorbate concentration between 5.6 x 10(-6) and 3.7 x 10(-4) mol L-1, when 0.1 mol L-1 KH2PO4 buffer at pH 5.0 and 25.0 degrees C was employed. The sensor stability was assessed, allowing 280 determinati ons without significant decrease in the response. The relative standard dev iation for vitamin C determination in pharmaceuticals samples by the propos ed method was about 10%. Considering these deviations, the results obtained for both the methods (spectrophotometric and potentiometric) were similar.