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Tetra Detector Array
A revolutionary, integrated multiple-detector device designed for the characterization of natural and synthetic polymers and copolymers, proteins, protein conjugates, excipients and other macromolecules. Comprised of modular Refractive Index, Ultra-Violet, Low Angle Light Scattering and Viscometer detectors.
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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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"I have purchased 7 GPC systems from Viscotek in Europe, US and Canada. I am very satisfied. The systems are robust and affordable. OmniSEC software is very user friendly and highly versatile."
- R.N., Academic Institution
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HTGPC
The Viscotek High Temperature GPC (HT-GPC) System is a revolutionary advanced detector system specifically designed for the characterization of polyolefins, natural and synthetic polymers, nanoparticles and other large molecules. |
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DLS Theory - Principle of DLS |
Dynamic light scattering (DLS - also known as Photon Correlation Spectroscopy) is a powerful technique, which can be used to determine the size distribution of small particles in solution.
When light hits small particles, it scatters according to the Rayleigh Equation -
provided the particles are small compared to the wavelength of the light.
DLS works by measuring the speed at which particles move under Brownian motion. A typical DLS System will shine a laser into a cell containing
the sample and measure the intensity of light scattered by the sample at some fixed angle. The intensity of scattered light will vary as the particles move around under
Brownian Motion
causing constructive and destructive interference of the light.
DLS uses the method of Autocorrelation to uncover important information buried in
the intensity fluctuations. Autocorrelation is a mathematical
means to measure of how well a signal matches a time-shifted version of itself,
as a function of the amount of time shift. In the case of DLS, the quicker the autocorrelation
function decays, the faster the particles are moving. The Autocorrelation function is formally
defined:
Where μ is the mean, σ is the standard deviation, X is the signal t is a counter,n is the number of data points, k is the amount of shift and R is the autocorrelation value.
The Autocorrelation of DLS data is best described visually:
 When applied to DLS data, the plot of the Autocorrelation function against the time shift is an inverse exponential.
By plotting the function against the log of the time-shift, we see the traditional
Autocorrelation function that is the basis for further DLS theory.
The general form of the DLS autocorrelation function is:
Where g2(t) is the Autocorrelation function,
A is an amplitude factor, Γ
is the decay rate and
t is the time-shift.
Γ is related to the Hydrodynamic Radius by the Stokes
Einstein equation:
The values in the Stokes Einstein equation are as follows:
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K |
Bolzman's constant |
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T |
Absolute Temperature |
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η |
Solvent Viscosity |
| RH
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Hydrodynamic Radius |
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n |
Refractive Index |
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λ |
Laser Wavelength |
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Φ |
Scattering Angle |
As can be seen, most of the values in the Stokes Einstein equation are either constant
or easily determined, leaving a simple relationship between Γ
and RH.
By taking the natural logarithm of the autocorrelation function, we can form a linear
relationship between the observed Autocorrelation value and Γ.
Thus it is a simple step to determine a single RH.
value from the experimental data. |
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