Abstract: Ion-selective eleltrodes(ISEs) are simple electrodechemical devices for the direct measurement of ions in the samples. A novel potentiometric biosensor for the determination of L-Malate or D-isocitrate has been developed by using CO2-3 -ISE-FIA system was composed of a pump, an injector, a malic enzyme or isocitric dehydrogenase enzyme reactor, a CO2-3 -ISE, a pH/mV meter, and an integrater. The various factors, such as buffer capacity types of plstericizer and polymer, were optimized for the CO2-3 selectivity. In this novel CO2-3 --ISE-FIA system, the potential difference due to the amount of CO2-3 produced from each enzyme reaction was proportional to the amount of L-malate or D-isocitrate.

Abstract: A potentiometric biosensor for the analysis of isocitrate was developed by using a CO32--selective electrode and enzyme immobilization in flow injection analysis (FIA). The biosensor consisted of a peristaltic pump, injector, enzyme reactor, reference electrode, working electrode, pH/mV meter and record. The experimental parameters that influenced the sensitivity and selectivity of the biosensors were optimized in the FIA system. A linear correlation between the potential difference and logarithmic isocitrate concentration was obtained in the range of 10^-3-10-1 M isocitrate under optimal conditions. The interference effect of major sugars and organic acids on the sensor system was less than 5%. Isocitrate concentrations of some fruit juices analyzed by the isocitrate sensor system were compared with those analyzed by gas chromatography (GC). There was no significant difference between the two analytical methods in any of the fruit juices. This suggests that the isocitrate sensor system is reliable in determining the isocitrate concentrations of foods.