POTENTIOMETRIC FLOW-INJECTION DETERMINATION OF UREA IN BLOOD SERUM USING ASYMMETRIC MEMBRANE ION-SELECTIVE ELECTRODE

Abstract

The potentiometric response of urea biosensor based on asymmetric cellulose triacetate membrane with nonactin and immobilized urease is strongly interfered by the presence of ammonium and potassium ions. The coveting of biosensor surface with microporous hydrocarbon anion-exchange membrane does not eliminate the cationic interferences sufficiently. The complete removal of interferences was obtained when fluorocarbon polymer anionic membrane was used either in a compact biosensor in wall-jet flow cell or in a separate dialyzer unit. For the latter case, in the optimized conditions of the flow-injection measurements, the lower detection limit of Nernstian response was 2mM urea. In measurements with maximum sampling rate 70 hr-l total removal of 10 mM potassium and 1 mM ammonium ion interference was obtained. Results of flow-injection urea determination in human blood serum samples were correlated with those obtained with Kodak EktaChem 700 clinical analyzer.