Abstract: Enzymes are useful as analytical reagents due to their selectivity and ability to catalyze reactions of substrates at low concentrations. Enzyme-based analyzes are successfully applied to various compounds, and considerable attention is given to the use of these reagents in flow-injection systems. Because no separation is involved in flow-injection analysis (FIA), the specificity of an assay can be achieved by using an enzyme that is specific for the analyte. Incorporation of the selectivity of an enzyme together with the simplicity, versatility, good precision, high sampling rate, low cost, and automation of FIA provides a useful system for a broad range of applications, particularly for the analysis of large numbers of samples in clinical laboratories. Purified enzymes suitable for analytical use are expensive, and large quantities of these reagents are consumed in the flow systems, making the cost of the analysis exceedingly high. The limited stability of enzymes in solutions may lead to poor reproducibility. These problems can be overcome by using immobilized enzyme reactors. The chapter discusses the use of immobilized enzyme reactors in FIA. Several typical applications with different types of reactors are also presented.

Abstract: Flow injection systems for the determination of H2O2 and glucose are described; both are based on the Fiatron SHS-200 microprocessor-controlled solution-handling system (Fiatron Systems Inc., Milwaukee, WI). The H2O2 oxidizes I- in the presence of starch and (NH4)6Mo7O24 for detection at 585 nm, the system being used in the stop - flow mode, and glucose is determined potentiometrically as H2O2 after passage through an immobilized-enzyme (glucose oxidase) reactor. The calibration graphs are rectilinear up to 8 µg mL-1 of H2O2 and 0.8 mg mL-1 of glucose.