SEC-MALLS stands for Size-Exclusion Chromatography Combined with Multiangle Laser Light Scattering.
When light passes through a medium such as a solvent, even a transparent one, interaction with the molecules leads to scattering off the axis of the light beam. This may be observed by a sensitive detector and its intensity measured at different angles to the beam. If a solute of different refractive index is present this will lead to an excess scattering dependent on the concentration of solute but also on its molar mass and for large particles, on the scattering angle. In a suitably calibrated system this may be used to determine the molar mass of the solute. The angular dependence for large particles (> 200KDa) may be used to estimate size (i.e. radius of gyration).
Because accurate concentration determination is vital for estimation of molar masses, the system also include a refractive index detector-proteins have a very consistent concentration effect on refractive index of solutions. Harnessing these two instruments to a chromatography system allows buffer before and after eluted peaks to be used as a very accurate reference baseline, avoiding the elaborate buffer matching required for accurate work on batch samples.
1) Solution molecular mass determination.
2) Size determination.