FIELD: measuring equipment.SUBSTANCE: invention relates to determining the amount of oxoanions in aqueous solutions. Method and system for determining the concentration of an oxoanion in an aqueous solution comprises source of an aqueous solution with an unknown concentration of oxoanion; source of an aluminum-containing reagent configured to supply the aluminum-containing reagent to the aqueous solution to form a solution for optical analysis; optical sensor, including an emitter, configured to direct light into a solution for optical analysis; detector, device configured to detect light transmitted through a solution for optical analysis and to provide an optical response, and a controller configured to determine the concentration of the oxoanion in an aqueous solution having an unknown concentration of an oxoanion based on the optical response of the solution for optical analysis.EFFECT: technical result is to ensure accurate and timely measurement of the concentration of oxoanion in the water stream.33 cl
