Determination of glucose in soft drinks using its enzymatic oxidation and the detection of formed hydrogen peroxide with a dinuclear iron(III) complex

Abstract

A new method for the determination of glucose in soft drinks based on the glucose oxidase-catalyzed oxidation of the analyte has been developed. Hydrogen peroxide is formed as by-product and is quantified by its immediate formation of a coloured adduct with a dinuclear iron(III) complex. Detection is performed at wavelengths between 570 and 600 nm. The method avoids the use of a second enzymatic reaction step. It has been optimized for the determination of glucose in soft drinks using microplate spectrophotometry and flow injection analysis (FIA) with spectrophotometric detection. The limit of detection (LOD) is 10 μmol/l (1.8 ppm), the limit of quantification 30 μmol/l (5.4 ppm) on microplates. Calibration functions are linear over a range from 30 to 200 μmol/l (5.4–36 ppm). Due to the low LOD, sample pretreatment even for coloured or turbid samples may be reduced to a dilution of the samples by a factor of 1000 with deionized water. In flow injection analysis, a reaction coil kept at 37°C provides for the required reaction time of 127 s. For the analysis of soft drinks, the new methods have proven to yield comparable results to two established methods for glucose analysis.