Chromatography Forum

Does SEC-MALS or DLS take into consideration the actual shape of the macromolecule? In other words, does it assume the molecule to be globular?

Molar mass determination by SEC-MALS makes no assumptions regarding shape. The rms radius or radius of gyration determined by MALS makes no assumptions about shape either, though it can be converted to an effective radius or length for certain shapes such as homogeneous spheres, shells, random coils or elongated rods.

DLS essentially determines diffusion coefficients, which are expressed in terms of the size of a sphere with the measured diffusion coefficient – the “hydrodynamic” radius. DLS only determines this effective size and, at best, can estimate molar mass by assuming a shape; e.g., globular or random coil.