A TRI-ENZYME ELECTRODE PROBE FOR THE SEQUENTIAL DETERMINATION OF FRUCTOSE AND GLUCOSE IN THE SAME SAMPLE

A new probe for the determination of fructose and glucose has been ass embled using a platinum electrode and three enzymes co-immobilized on its surface: fructose dehydrogenase, glucose dehydrogenase and diaphor ase. The mechanism of this probe is very simple: when the probe is imm ersed in a solution containing fructose and glucose and an electrochem ical mediator, the current signal is due to the fructose. Then, by add ing NAD(P)(+) a current response due to the glucose present in solutio n is obtained. Analytical parameters such as pH, buffer, temperature, concentration of mediator and ratio of the three enzymes co-immobilize d have been optimised. Probe stability and reproducibility have been e valuated. Calibration curves for fructose and glucose have been constr ucted and all analytical parameters optimized. The linear range for bo th fructose and glucose was from 5x10(-6) to 2x10(-4) mol/L and the de tection limit was 1x10(-7) mol/L. The probe has been used to determine the concentration of fructose and glucose in ten different samples of honey. The values obtained were compared with those obtained by UV-VI S spectrophotometry and the results were in good agreement.