The most common method of using a MALS is to connect to a HPLC size exclusion chromatography (SEC) or gel permeation chromatography (GPC) system, such as OMNISEC. As part of this system it is essential that a concentration detector, Refractive index or UV, is also connected.
The Viscotek SEC-MALS detector measures the light scattered by a sample at many angles and for a Debye plot to be created. The Debye plot models the angular dependence of a samples scattering and is used to determine the Mw and Rg at every data slice within the chromatogram. Importantly the fit order and model chosen for this analysis needs to be carefully considered as it will have a significant impact on the results. Isotropic scatterers, smaller than 10-15nm in radius, will scatter light evenly in all directions meaning only the Mw can be measured. Anisotropic scattering samples, more than 10-15nm in radius, will scatter more light in the forward direction allowing both Mw and Rg to be measured. Using the Rg a conformation plot can be generated (plot of Rg against Mw) which allows any structural differences between samples to be measured.