A simple FIA-system for simultaneous measurements of glucose and lactate with amperometric detection

A flow injection system for the simultaneous amperometric determination of glucose and lactate is described. Glucose oxidase and lactate oxidase were immobilized, separately, into two-parallel immobilized enzyme reactors (IERs). The enzymatically produced hydrogen peroxide was detected by anodic amperometry at platinum electrodes coated with an electropolymeric-permselective layer of m-phenylenediamine to enhance the selectivity of H₂O₂ detection. The configuration of the flow system was designed to give a response output in the form of a train of two successive peaks. The heights of these two peaks were directly proportional to the concentration levels of glucose and lactate in the sample, respectively. The presented flow system proved to offer the advantages of i) simplicity, ii) operational stability, up to 3 months, iii) simultaneous determination of glucose and lactate using a single 20-μL sample injection iv) insensitivity of the signal of a given component by wide variations in the concentration of the second component, v) high sample throughput, more than 50 samples/hour, vi) high accuracy and precision, and vii) a reasonable dynamic range of about two-orders of magnitude. The reliability of the present system was assessed by measuring glucose and lactate simultaneously in several samples of blood plasma, urine and dairy products. The obtained results were in good agreement with those obtained by standard spectrophotometric methods.