An amperometric flow-injection biosensor system was developed for the simultaneous measurement of creatinine, glucose, and urea, with a single sample injection and one detector. The principle for the amperometric detection of urea and creatinine was based on coupled reactions of three sequentially aligned enzyme reactors, urease or creatinine deiminase/glutamate dehydrogenase/L-glutamate oxidase. Inclusion of a split point and two confluence points between the injector and detector (oxygen electrode) resulted in a flow-injection system composed of three channels. Triple peak recording was obtained by putting two delay coils of different lengths at the channels involving urease and glucose oxidase. The system gave linear calibrations for creatinine, glucose, and urea in the ranges of 0.2–5, 0.2–10, and 0.5–20mM, respectively. The assay procedure was simple and one run was completed within 4 min. The system was reproducible within 5–8% of relative standard deviation.
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