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

A flow 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 1.0×10−3 and 1.0×10−2 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.