This work introduces a novel method, label dilution, which is analogous to the well-established isotope dilution method. The principle is tested on a model system of commercially available antibodies and protein-coated Sepharose beads and implemented using micro-bead injection in the lab-on-valve format. This micro-scale method uses a labeled form of the target molecule as an internal standard. Label dilution employs ratiometric measurements using the absorbance signals from the label and the target molecules for quantitative determination of an analyte. The label dilution method is shown to discriminate between selective and non-selective binding and provides a means for monitoring bioligand interactions in real time. With a detection limit of 470 ng of IgG, this method provides a sensitive, automated technique for the determination of low-level analytes in complex samples. This technique has been developed with the aim of using it to facilitate diabetes research in which the interactions between autoantibodies and the molecules they target are a central focus.