A flow-injection biosensor system for the amperometric determination of creatinine: simultaneous compensation of endogenous interferents.

A flow-injection biosensor system was developed for the amperometric determination of creatinine based on coupled reactions of three sequentially aligned enzyme reactors, creatinine deiminase, glutamate dehydrogenase, and glutamate oxidase, using an oxygen electrode as the detector. To overcome the problem of endogenous ammonia and glutamate, the flow was split into two channels after the injector and rejoined before the glutamate dehydrogenase reactor. Double peak recording was obtained by setting a delay coil and a reference column in one of the two channels. The first peak gave the sum response of creatinine, endogenous ammonia, and glutamate, and the second that of endogenous ammonia and glutamate. By this method compensation for endogenous ammonia and glutamate, as well as for interfering ascorbic acid, was achieved simultaneously. The system gave linear calibrations up to 2 mM for the first peak and 3 mM for the second one. The lower detection limits were 0.1 and 0.02 mM for 35- and 100-microliters injection of sample, respectively. One run was completed within 2 min. The system showed good reproducibility (< 3%) and long operational stability (> 1300 runs). The assay results of creatinine in urine showed good correlation with those obtained from the chemical method of Jaffe.