Abstract: A review with 17 references. A few examples from the recent literature are introduced, including flow-injection anal., the stop-flow method, and flow-through titration (SFS)

Abstract: Two flow injection manifolds are described. In the first, glutamate dehydrogenase was used to remove endogenous NH3, then the mixture passed through three reactors containing creatinine deiminase (to produce NH3 from creatinine), leucine dehydrogenase (to convert NH3 to L-leucine) and L-amino-acid oxidase, respectively; L-leucine oxidation was monitored using an O2 electrode. In the alternative system, a two-channel approach was used in which endogenous NH3 and L-amino acids were simultaneously compensated for with a two-channel system based on the principle of split and confluence of flow (details given). The methods were applied to determine creatinine in urine. For the single-channel system, the response time was ~1 min, the calibration graph was linear for up to 5 mM creatinine and the detection limit was 0.2 mM; the results correlated well with those obtained by the Jaffe method. With the two-channel system (less expensive to operate) the sensitivity was improved and the results correlated well with those obtained by the Jaffe method.

Abstract: A single-channel and a dual-channel flow injection system are described and illustrated. The method involved the urease-catalyzed hydrolysis of urea or the creatinine deiminase-catalyzed hydolysis of creatinine to yield NH3, and amperometric detection of the NH3 via coupled enzymatic reactions in which (i) 2-oxoglutarate was reduced to L-glutamate and H2O2 in the presence of NH4+, NAD(P)H and glutamate dehydrogenase, and (ii) the L-glutamate was re-oxidized in the presence of glucose oxidase; the consumption of O was detected with an O electrode. Each of the enzymes was immobilized on modified controlled-pore glass and packed into a glass tube for use in the flow systems. With use of the dual-channel system to determine urea and creatinine simultaneously, the response was rectilinear from 0.1 to 5 mM analyte, and the coefficient of variation (n = 12) were 5%. 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 creatine 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. Double-peak 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.