The molecular size or hydrodynamic radius RH can be determined in two ways. The first method is by Dynamic Light Scattering (DLS), which is generally used as a batch technique to measure the average size in the whole sample, but can be used as a detector for Size Exclusion Chromatography (GPC/SEC).

When measuring molecular size a very accurate and precise method of obtaining RH of all components in a sample is by triple detection after separation by SEC.

By the use of online light scattering and viscometer detectors, the MW and intrinsic viscosity of the polymer or protein can be determined and hence the RH calculated at any point on the chromatogram.

The benefit of both these techniques is that there is no practical upper or lower size limit for the materials being investigated.

The measurement of molecular size is a useful parameter for a number of applications:

  • Comparison with molecular weight gives information about structure
  • DLS can use molecular size to give a quick estimate of molecular weight
  • DLS can give a fast screen of protein purity
  • Determination of protein melting point.

OMNISEC

Viscotek SEC-MALS 20

Zetasizer range

Empyrean Nano Edition

OMNISEC Viscotek SEC-MALS 20 Zetasizer range Empyrean Nano Edition

The world’s most advanced multi-detector GPC/SEC system

Multi angle light scattering detector

The world’s most widely-used systems for nanoparticle, colloid and protein size and charge measurements

Versatile X-ray scattering platform

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Measurement type
Molecular structure
Molecular size
Molecular weight
Technology
Gel Permeation Chromatography
Size Exclusion Chromatography (SEC)
Dynamic Light Scattering
X-ray Diffraction (XRD)