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Dear CCP4 board I have a protein that exists in equilibrium between monomer and dimer and I'm trying to calculate KD using size exclusion. The problem is that the column dilutes my sample so that if I put 20 uM on to the column, I only recover 0.5 uM in dimer fraction and 2 uM in monomer fraction. I am getting confused as to how to plot my KDs. Do I not regard my initial concentrations at all and work only with the final concentrations that come off the column? I would plot [monomer] squared vs [dimer] and I will assume that the ratio of monomer to dimer will stay constant as the protein passes through the column. (also I would calculate [dimer] using 2x monomer extinction coefficient) Does this seem a reasonable way to calculate KDs and reasonable argument? Also I am looking for good references for calculating Kds when dealing with dimerization Thanks and sorry for off topic question Careina