A method for measuring the concentration of a chemical species using a reagent baseline

A method in which a concentration of a chemical species of interest is obtained. The method comprises measuring a property (e.g. the oxidation reduction potential) of a reagent (typically based on a simple single electron redox couple) to obtain a baseline measurement. The reagent is mixed with the solution under test, then the property of the mixture is measured to obtain a post reaction measurement. Then the concentration of the chemical species of interest is determined based on the baseline measurement and the first post reaction measurement, typically by calculating a difference of the baseline measurement and the post reaction measurement, then using the difference and a pre-determined conversion table to determine the concentration of the chemical species of interest.