Enzyme sensor system for potentiometric urea determination in serum and milk

Abstract

A potentiometric enzyme electrode system for rapid assay of urea in biological fluids such as serum and urine, using a dual pH electrode arrangement in differential measuring mode is described. Individual sample pH correction within a fixed-time measuring interval provides both a good correlation with the indophenol method (correlation coefficients r = 0.998 and r = 0.987 for serum and milk, respectively) and a reasonable sample throughput (20–25 samples/h). A linear response is obtained in the urea concentration range 1–20 mmol/1. Lyophilized soy urease (3 U/mg) is immobilized directly on the active surface of a pH glass electrode.