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"The GPCmax and Triple Detector System is state-of-the-art while remaining affordable and easy to use."
- M. G., Ph.D., Academic Institution
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Application Notes
Our database of GPC/SEC application notes explain the use of concentration, viscometer and light scattering detectors to obtain a distribution of absolute molecular weight, size and intrinsic viscosity, as well as information on conformation, aggregation, branching and copolymer composition.
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Product Brochures
Download product information from our extensive catalog of product literature.
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Nanoparticle and Protein Sizing
Viscotek is proud to introduce its range of Dynamic Light Scattering Detectors featuring rapid, accurate and sensitive sizing for proteins, biomolecules, nanoparticles & polymers and a pair of outstanding technologies unique to Viscotek. |
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GPC Theory: Polymer Structure |
The so-called radius of gyration (Rg) can be obtained by light scattering detection at several angles θ. This is done by determining the initial slope of the plot of the inverse light scattering intensity against sin2(θ/2).
However, angular dependence occurs only in the case of polymers whose coil diameter is greater than about 1/20 of the wavelength of the light. This corresponds to Rg of approximately 15 nm and, in the case of polystyrene, to MW of approximately 150,000 g/mol. Below this limit, the light cannot resolve any structure, and determination of the Rg is not possible.
In the case of branched polymers, the limit is located at markedly higher molecular masses, since these possess a substantially higher molecular density. In addition to this limitation at low molecular size there is a further problem at the upper end. Large polymers often display a non-linear angular dependence of the inverse light scattering intensity, so that the initial slope (and hence the Rg) cannot be reliably determined by multi-angle light scattering.
As we've seen in Universal Calibration, the intrinsic viscosity, IV, of polymer samples is measured by means of GPC
viscosity detectors. As the reciprocal density of the polymer coil in solution, IV represents a direct, sensitive structural parameter and, therefore, a traditional parameter in the polymer industry.
The well-known Mark-Houwink plot:
IV = K · MWa
can be obtained by means of the double-logarithmic plot of intrinsic viscosity against MW. The Mark-Houwink plot is the central plot of polymer structure analysis. It reflects structural changes in the polymer, such as branching and chain rigidity. The slope, described by the Mark-Houwink exponent a can vary between 0 for solid spheres and 2 for rod-shaped structures.
Analogous to the Mark Houwink plot, the so-called conformation plot can be constructed from light scattering data by plotting Log Rg against Log MW. Its slope can only vary between 0 and 1. For this reason, structural changes are much more evident from viscosity detection. Generally speaking, structural parameters can be determined more directly, in a wider MW range, and are more easily reproducible, by means of
viscosity detection than by
light scattering.
Combining the advantages of both detectors leads to
triple detection (RI/Viscosity/LS): molecular masses can be determined by light scattering, and structure information through intrinsic viscosity. In addition, this combination makes it possible to determine and differentiate between aggregates and microgels.
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