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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 properties of copper (II) ions occluded in EVA membrane was developed for L-ascorbic acid determination. The poly-ethylene-co-vinyl acetate (EVA 40% m/m) matrix was doped with copper (II) ions and dispersed on the surface of a graphite/epoxy tubular electrode. The electrode showed a super-Nernstian response for L-ascorbic acid concentration between 10-3 and 10-1 mol L-1 with a detection limit of 8.5×10-4 mol L-1, when 0.1 mol L-1 KH2PO4 buffer mixed 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 per hour with a precision of 3.6%. The results obtained for ascorbic acid determination in pharmaceutical samples, without any previous treatment, were similar to those obtained by the British Pharmacopoeia method.

L-ascorbic acid determination; tubular electrode; FIA; pharmaceutical samples


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