The intensity of light scattered by a solution is directly proportional to the average molecular weight and to the concentration of its components. The PFBMI has a multiple detector (OMNISEC GPC/SEC, Malvern), coupled to a GPCmax size-exclusion chromatography system. Apart from a multi-angle light scattering detector, this instrument includes a refractometer/UV-visible spectrophotometer and a viscometer. This on-line setup allows the simultaneous determination of the molecular weight of each component of a solution, which is particularly useful to characterize the size and the stoichiometry of molecular assemblies in different experimental conditions. The study of intrinsic viscosity also allows to gain insight into macromolecular shape and hydration parameters.