While online multi-angle light scattering (MALS) is one of the most important techniques for macromolecular characterization, it can be made even more versatile with the addition of a quasielastic light scattering (QELS, a.k.a. dynamic light scattering) module for determination of hydrodynamic radius. QELS can be added to a Wyatt MALS system as a WyattQELS™ module embedded in the MALS instrument, or by connecting the MALS flow cell to a batch DLS instrument such as a DynaPro® NanoStar® or Mobius® via optical fiber. The QELS instruments can be used to determine the hydrodynamic radius, rh , for a variety of samples in a continuous-flow mode. The combined MALS-QELS system will measure simultaneously rg , rh , and the absolute molar mass.
Since rg (the root mean square radius) is determined directly from the angular dependence of the scattered light intensity, at least three angles are required to make a reliable measurement. On the other hand, rh is derived from the fluctuations of light scattering intensity due to diffusion of the molecules (aka Brownian motion) and a single measurement angle suffices.
