On-line monitoring of monosaccharides and ethanol during a fermentation by microdialysis sampling, liquid chromatography and two amperometric biosensors

Two amperometric biosensors were used as detection units in liquid chromatography for on-line monitoring of the production of fuel ethanol during a fermentation. Sampling was performed with a microdialysis probe, and the dialysate was introduced into a liquid chromatographic system providing separation of the substrates and the product: three monosaccharides and ethanol. The analytes were detected by two carbon paste electrodes based on pyranose oxidase and alcohol oxidase, respectively, co-immobilised with horseradish peroxidase, operating in parallel at -50 mV vs. Ag/AgCl. The measured linear ranges of the biosensors by direct injection into the LC system were for glucose 0.3-2.5 g L-1, xylose 0.5-6.7 g L-1, galactose 0.5-6.7 g L-1, and ethanol 1.6-11.7 g L-1 and the detection limits were 0.1, 0.2, 0.4, and 0.2 g L-1, respectively. Injection of standard solutions were required to monitor the stability of the biosensors. Due to the strict selectivity of the biosensors, no interference from other compounds in the broth was encountered in the quantification. The fermentation process was monitored for 16 h. The on-line results were compared with off-line measurements.