Potentiometric enzyme electrode in a flow injection system for the determination of urea in human serum samples

A urea biosensor with urease covalently bound directly to the membrane of the ammonium ion selective electrode has been developed. The enzyme electrode was tested in single and double channel how injection analysis (FIA) systems. Optimised measurement conditions allowed determination of urea within the linear range of 0.5-8 mM in the single channel and of 1-10 mM in the double channel FIA system. The response time of the biosensor was short enabling frequent sample injections (every 1.5-3 min). Long term stability of the enzyme electrode allows application of the same biosensor in the FIA systems for up to two months. Under optimised conditions the determination of urea is possible at physiological and pathological levels. The results of urea determination in real, human serum samples were in good agreement with those obtained by routine clinical analysis methods. (C) 1998 Elsevier Science B.V. All rights reserved.