The determination of the scattering density distribution of polydisperse solutions by contrast variation: a neutron scattering study of ferritin

From the dependence of zero-angle scattering of polydisperse solutions on the scattering density of the solvent, information about the mean scattering density and the width of the scattering density distribution of different dissolved molecules can be obtained. This method has been tried with a commercial solution of native ferritin. The root-mean-square deviation of the scattering density was 0.35 × 10¹⁰ cm^-2 with respect to the mean value of 3.15 × 10¹⁰ cm^-2. From these data the mean saturation of native ferritin with iron is estimated to about 0.6 and the root-mean-square fluctuation of the iron contents of different ferritin molecules to about 0.4. The neutron scattering curves agree with the results from X-ray small-angle scattering.