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

A new method for the determination of glucose in soft drinks based on the g lucose oxidase-catalyzed oxidation of the analyte has been developed. Hydro gen peroxide is formed as by-product and is quantified by its immediate for mation of a coloured adduct with a dinuclear iron(III) complex. Detection i s performed at wavelengths between 570 and 600 nm. The method avoids the us e of a second enzymatic reaction step. Tt has been optimized for the determ ination of glucose in soft drinks using microplate spectrophotometry and fl ow injection analysis (FIA) with spectrophotometric detection. The limit of detection (LOD) is 10 mu mol/l (1.8 ppm), the limit of quantification 30 m u mol/l (5.4 ppm)on microplates. Calibration functions are linear over a ra nge from 30 to 200 mu mol/l (5.4-36 ppm). Due to the low LOD, sample pretre atment 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 ana lysis, a reaction coil kept at 37 degrees C provides for the required react ion time of 127 s. For the analysis of soft drinks, the new methods have pr oven to yield comparable results to two established methods for glucose ana lysis. (C) 1999 Elsevier Science B.V. All rights reserved.