Development of a new FIA-potentiometric sensor for dopamine based on EVA-copper(II) ions

A how injection analysis (FIA) system using a tubular electrode based on the redox properties of copper(II) ions immobilized in a poly(ethylene-co-vinyl acetate) (EVA) membrane was developed for dopamine determination. The Cu2+ was trapped in the EVA (40% m/m) matrix and dispersed on the surface of a graphite-epoxy flow-through electrode. The electrode based on the dopamine oxidation catalyzed by Cu2+ exhibited a near-Nernstian response (83.2 +/- 0.2 mV decade(-1)) for dopamine concentration between 1.0 x 10(-3) and 1.0 x 10(-2) mol l(-1) (r = 0.9992), employing 0.25 mol l(-1) KH2PO4 buffer, containing 0.1 mol l(-1) H2O2 at pH 7.0, as a carrier solution. The potentiometric-FIA system allows an analytical frequency of about 25 samples per hour with a good precision (variance lower than 4.2%). The best potentiometric response was achieved using an EVA membrane containing 5.0% (m/m) Cu2+ ions. The use of hydrogen peroxide in a flow-system makes an efficient reoxidation of the Cu1+ ions possible in the EVA membrane. The relative standard deviation for dopamine determination in pharmaceutical samples, without any previous treatment, was about 4.7%. The useful lifetime for the dopamine sensor was longer than 3 months, in continuous use, (C) 2000 Elsevier Science S.A. All rights reserved.