Size and Molecular Weight Analysis

For micro/nanoparticles or macromolecules in solution, their molecular weight and size are of great interest to people. For example, those information strongly affects the property of polymer and its end applications. A High molecular weight increases the chemical resistance of polymer, which means it takes more damage to the main chains of the molecules before it will affect the strength of the material. The viscosity of the polymer increases with its molecular weight – makes it harder to process the material using conventional methods. GPC-MALS is the most effective, accurate and widely used technique to determine molar mass of polymers in solution so far. It is a combination of gel permeation chromatography (GPC), multi-angle light scattering (MALS) and other instruments that work together to provide the optimum performance. GPC measures the relative molecular weight by separating macromolecules in the solution based on their size. The column used for GPC is filled with a microporous gel material. Due to the difference in travel distance, smaller molecules have longer elution time than larger size molecules. MALS detects scattered light intensity of the macromolecule in the solution. Based on Rayleigh theory, larger molecules scatter more light than smaller molecules from a given light source and that the intensity of the scattered light is proportional to the molecule’s molecular weight. It is necessary to relate the intensity of the light to the molecular weight of molecules, so the molecular weight of your sample measured by MALS is determined on the basis of the reference sample, usually polystyrene with a known molecular weight.

Dynamic light scattering (DLS) determines the size distribution profile of molecules or nanoparticles in solution by quantifying dynamic fluctuations in the intensity of scattered light from moving particles. The fluctuations are directly related to the rate of diffusion of the molecule through the solvent, which is related in turn to the particles' hydrodynamic radius. Via the Stocks-Einstein equation, the size can be determined. Light scattering based techniques have also been extensively used in characterizing molecular interactions such as protein aggregation, oligomerization and the kinetics of self-assembly. At Matexcel we can provide you with a complete package of solutions for molecular weight and particle size measurement.

Viscotek Triple Detector Array system (TDA 305) incorporates Refractive Index (RI), Light Scattering (LS) and Viscosity (VIS) detectors.

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