Urease coupled to poly(vinyl alcohol) activated by 2-fluoro-1-methylpyridinium salt: preparation of a urease potentiometric electrode and application to the determination of urea in serum

Abstract

A urease electrode is described for the determination of urea in serum samples. The electrode was prepared by chemically immobilizing urease to 2-fluoro-1-methylpyridinium toluene-4-sulphonate-activated poly(vinyl alcohol) and physically adsorbing the resulting conjugate directly on to the hydrophobic membrane of an ammonia gas-sensing electrode. Linear calibration was obtained over the range 10 −4–10 −1 M urea. The recovery varied between 97 and 102%. The within-day relative standard deviation (R.S.D.) was 1.2–2.7% and the day-to-day R.S.D. was 2.9–4.5%. There was only a 14% decrease in electrode activity over a period of 28 days. Up to 30 serum samples can be analysed per hour.