Abstract: Apparatus, systems and methods for measurement of B22 values of proteins in aqueous solutions in flow-mode utilize a dual-detector cell are provided. Simultaneous measurement of protein concentration and scattered light intensity is facilitated as the protein elutes from a size-exclusion column. Each data point on the resulting chromatograms is converted to Rayleigh's ratio, R?, and to concentration c, respectively. The B22 value is calculated from the slope of the Debye plot (Kc/R? versus c) generated from a range of the concentrations obtained from these chromatograms for a single protein injection. Measurements may be analyzed using modeling data derived from a predetermined modeling equation to quantify self-association of molecules. The apparatus and method provide a reliable means for determining B22 values for such proteins as lysozyme, chymotrypsinogen, and chymotrypsin in various solution conditions.