Amperometric Flow-injection Biosensor System for the Simultaneous Determination of Urea and Creatinine

A flow-injection biosensor system was developed for the simultaneous assay of urea and creatinine, with a single injection and one detector. The amperometric detection of urea or creatinine was based on coupled reactions of three sequentially aligned enzyme reactors, urease or creatinine deiminase, glutamate dehydrogenase and glutamate oxidase. Ammonia produced by the enzymatic hydrolysis of urea or creatinine was converted to glutamate, and the oxygen consumption due to the oxidation of glutamate by glutamate oxidase was detected with an oxygen electrode. A split and confluence of the flow stream between the injector and the glutamate dehydrogenase reactor resulted in a two-channel system. Doublepeak recording was achieved by putting a delay coil at one of the two channels. The system gave linear calibration curves over a range of 0.1-5.0 mM for both urea and creatinine. The assay procedure is simple and one run can be completed within 3 min. The system was reproducible within 5% of the relative standard deviation.