Abstract: The present invention relates to a method for quantitatively measuring concentration in aqueous solution A of chemicals, functionalized with at least one tracer, comprising at least the following successive steps of (a) impregnating a flow assay containing at least one test area, that detects the tracer functionalizing the chemicals to be quantified, with solution A, (b) introducing the flow assay into a test reader, and (c) using the test reader.