Patent ID: 7431820

Claim:
A method for determining a concentration of a reduced or oxidized form of a redox species, the method comprising the steps of: a) providing an electrochemical cell comprising a first working electrode, a first counter electrode, a second working electrode and a second counter electrode; b) selecting a spacing between the first working electrode and the first counter electrode such that reaction products from the first counter electrode arrive at the first working electrode; c) selecting a spacing between the first working electrode and the second counter electrode such that a significant amount of reaction products from the second counter electrode do not arrive at the first working electrode; d) selecting a spacing between the second working electrode and the second counter electrode such that a significant amount of reaction products from the second counter electrode do not arrive at the second working electrode; e) applying an electric potential difference between the first working electrode and the first counter electrode; f) applying an electric potential difference between the second working electrode and second counter electrode; g) selecting a potential of the first working electrode such that a rate of electro-oxidation of a reduced form of a redox species or a rate of electro-reduction of an oxidized form of a redox species is diffusion controlled; h) selecting a potential of the second working electrode such that a rate of electro-oxidation of the reduced form of a redox species or a rate of electro-reduction of an oxidized form of a redox species is diffusion controlled; i) subtracting a current flowing between the second working electrode and the second counter electrode from a current flowing between the first working electrode and the first counter electrode, whereby a corrected current is obtained; and j) obtaining from the corrected current a value indicative of the concentration of the reduced form of the redox species or the oxidized form of the redox species.