Pulsed-amperometric detection of urea in blood samples on a conducting polypyrrole-urease biosensor

A rapid and highly sensitive method is described for reliable flow injection analysis of urea based on pulsed-amperometric detection with a polypyrrole-urease biosensor. The optimum conditions were 0.05 M phosphate buffer (pH 7.0), a negative potential pulse between −70 mV (E1) and −400 mV (E2) vs Ag/AgCl, a pulse width of 120 mS, and a flow rate of 0.1 ml min−1. A detection limit (3σ) of 60 μg l−1 of urea was achieved by this method and the response was linear in the range 100–4500 μg l−1. The biosensor was very stable in the flow system, even after two weeks of continuous use. Excellent recovery of urea (95%–112%) was accomplished employing this method in simulated samples. Successful application of the method to the determination of urea in blood plasma is reported.