ONLINE GLUCOSE MONITORING BY USING MICRODIALYSIS SAMPLING AND AMPEROMETRIC DETECTION BASED ON WIRED GLUCOSE-OXIDASE IN CARBON-PASTE

In-vitro on-line glucose monitoring is described, based on microdialys is sampling and amperometric detection operated in a flow-injection sy stem. Samples were injected into a two-electrode microcell containing an Ag/AgCl quasi-reference electrode and a glucose enzyme electrode as the working electrode, operated at +0.15 V vs. Ag/AgCl. The enzyme el ectrode is constructed by mixing the 'wired' glucose oxidase into carb on paste. {Poly[1-vinylimidazole osmium(4,4'-dimethylbipyridine)(2)Cl) ]}(+/2+) was used to 'wire' the enzyme. The non-coated electrodes, cro ss-linked with poly(ethylene glycol) diglycidyl ether, responded linea rly to glucose concentrations up to 60 mM, and were characterized by a sensitivity of 0.23 mu A mM(-1) cm(-2), when operated in flow injecti on mode and of 5.4 mu A mM(-1) cm(-2) in steady-state conditions. This sensitivity of the resulting enzyme electrode was 50% lower than that of similarly prepared but non-cross-linked electrodes. However, the c ross-linked electrodes showed superior operational and storage stabili ties, which were further improved by coating the electrodes with a neg atively charged Eastman AQ film. An in-house designed microdialysis pr obe, equipped with a polysulphone cylindrical dialysis membrane, yield ed a relative recovery of 50-60% at a perfusion rate of 2.5 mu l/min(- 1) in a well stirred glucose solution. The on-line set up effectively rejected common interferences such as ascorbic acid and 4-acetaminophe n wizen present at their physiological concentrations.