The invention relates to a method of determining the binding site specificity of an analyte to a ligand having at least two different binding sites, which method comprises immobilizing the ligand to a solid support, mixing the analyte with a reversibly binding reference analyte which has a dissociation behaviour that differs significantly from that of the analyte, contacting the mixture with the ligand to determine dissociation characteristics for the mixture, and determining therefrom the binding site specificity of the analyte in relation to the reference analyte. The invention also relates to an analytical system for carrying out the method, and to a computer program, computer program product and computer system for performing the method.