Glucose oxidase (G.O., E.C.1.1.3.4) was immobilized into polyacrylamide gel tube (i.d., 3 mm) and a flow injection system with this tube reactor was fabricated to allow the determination of high concentration of glucose and to extend a linear range of the calibration curve. A Sample solution was passed through the tube reactor, and hydrogen peroxide produced by the enzyme reaction (1) was electro chemically oxidized on a platinum wire electrode at +0.6 V vs. SCE.
Glucouse G.O. → Gluconic acid + H₂O₂ ……… ( 1 ) The peak height of the current was proportional to the concentration of glucouse. The linear range of the calibration curve could be extended by varying either sample flow rate or sample volume, and 5 × 10^-4 2 M glucose could be determined directly. The relative standard deviation was about 2%. The time reguired for the analysis of each sample was about 2 min, where sample flow rate was 8.4 ml/min and sample volume was 5 pi. The half life of the immobilized enzyme activty was about one month and more than fifteen hundreds samples could be determined by the same immobilized enzyme tube reactor.