Potentiometric determination of L-ascorbic acid in pharmaceutical samples by FIA using a modified-tubular electrode

A flow injection system using a tubular electrode based on the redox proper ties of copper (II) ions occluded in EVA membrane was developed for L-ascor bic acid determination. The polyethylene-co-vinyl acetate (EVA 40% m/m) mat rix was doped with copper (II) ions and dispersed on the surface of a graph ite/epoxy tubular electrode. The electrode showed a super-Nernstian respons e for L-ascorbic acid concentration between 10(-3) and 10(-1) mol L-1 with a detection limit of 8.5x10(-4) mol L-1, when 0.1 mol L-1 KH2PO4 buffer mix ed with 0.1 mol L-1 hydrogen peroxide at pH 5.0 was employed as carrier The Potentiometric-FIA system allows an analytical frequency of 120 samples pe r hour with a precision of 3.6%. The results obtained for ascorbic acid det ermination in pharmaceutical samples, without any previous treatment, were similar to these obtained by the British Pharmocopoeia method.