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Abstract

An apparatus is provided for measuring the concentration of a substance in a sample solution. The apparatus comprises first electrode means, second electrode means and an enzyme channel between the first and second electrode means. The enzyme channel contains an enzyme for catalyzing a reaction of the substance whose concentration is to be measured. In use, a known volume of the sample solution is presented to the first electrode means in a test solution including an excess of a mediator, one of reduction or oxidation of the mediator being coupled to the reaction of the substance. The first electrode means is arranged to ensure that the mediator is respectively completely oxidized or reduced, and also to remove any interferent species. The test solution is then passed through the enzyme channel so as to permit reaction of all of the substance present in the solution, whereby a quantity of the mediator is respectively reduced or oxidized. The test solution is then presented to the second electrode means which are arranged to respectively oxidize or reduce the quantity of mediator which had been respectively reduced or oxidized. This produces a quantity of charge through the second electrode means which is measured by means for measuring said quantity of charge.

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