A method of quantitatively determining the concentration of at least one analyte in a sample by: (i) adding a portion of the sample to a first analyte assay formulation and to an analyte assay reference formulation to generate a first analyte sample and analyte reference sample and determining the concentration of the at least one analyte in the sample; and/or (ii) adding a portion of the sample to a second analyte assay formulation and determining the concentration of the at least one analyte in the sample, as well as formulations, kits of parts, systems and computer implemented methods associated with the method.