Quasi-elastic light scattering distributions

Recently, a four-laboratory cooperative study has led to a comparison of the determination of particle size distribution by electron microscopy, quasi-elastic light scattering and wide angle light scattering (20). 

Using Quasi-Elastic Light Scattering To Study Particle Size Distributions in Submicrometer Emulsion Systems... 

Quasi-elastic light scattering is an excellent technique for studying the formation and stability of submicrometer emulsions. Improvements in the methods of quasi-elastic light scattering data acquisition and analysis that enable full particle-size distribution studies of sub-micrometer emulsion systems are discussed. Using several oil/water emulsion systems as examples, we demonstrate the ability of these techniques to determine the effect of emulsifier concentration on the particle-size distribution produced by an inversion method of emulsification. Some of the benefits of obtaining the full distribution are also discussed. 

An alternate approach for determining particle density involves fraction collection followed by the application of quasi-elastic light scattering (QEL) to the fraction (19). The QEL technique is particularly effective in providing a mean particle diameter d for narrow particle distributions. With this d and the X obtained from V (the volume at which the fraction was collected), Ap can be calculated directly from Equation 3. 

Generally, mean size and size distribution of nanoparticles are evaluated by quasi-elastic light scattering also named photocorrelation spectroscopy. This method is based on the evaluation of the translation diffusion coefficient, D, characterizing the Brownian motion of the nanoparticles. The nanoparticle hydro-dynamic diameter, is then deduced from this parameter from the Stokes Einstein law. 

Figure 4. Apparent distributions of equivalent Stokes diameters, from quasi-elastic light scattering analysis of mixtures of 1.0 g/L PDMDAAC and 6.7 g/L BSA, in 0.01 M NaOAc buffer, at pH values shown.

This is also known as photon correlation spectroscopy (PCS) or quasi-elastic light scattering (QELS). It uses scattered light to measure the rate of diffusion of protein particles in a sample. The data on molecular motion are digitally processed to yield a size distribution of particles in the sample, where the size is given by the mean Stokes radius or hydrodynamic radius of the protein particles this is the effective radius of a particle in its hydrated state. Clearly, the hydrodynamic radius depends on both mass and shape. 

Particle size distributions have been reported with another new method, quasi-elastic light scattering. This method is most useful for the average particle size of monodisperse systems. Mathematical transforms are used to resolve polydisperse distributions, but no physical separation takes place. This method seems to work satisfactorily if the dispersion around each maximum in the polydisperse sol is narrow and the peaks are well separated in particle size. 

In the particular case of a bimodal particle size distribution where the second size is very small, detection can be difficult This is illustrated by the data in Table 12.13, which shows that the bimodal characteristic was measured by transmission electron microscopy (TEM), capillary hydrodynamic fractionation (FlowSizer), and by SFFF, but not by quasi-elastic light scattering (NICOMP 270 or Brookhaven B 1-90). While QELS (or PCS) instruments are capable of... 

This method allowed to establish, that besides adsoption layer buildup at the interface the protein solution-organic phase, the distribution of the protein between hquid phases takes place. BSA and a-chymotrypsin at aqueous the protein solution-toluene were investigated in detail [155,156]. Transfer of the protein from the solution into interface layer as well as into organic phase was shown. In [157] the average hydrodynamic radius (r) of associates of BSA with non polar molecules in the adjacent phases of aqueous solution and hydrocarbon were determined by the quasi-elastic light scattering method. Results are given in Table 9. 

The birefringence decay and the autocorrelation function decay (from quasi-elastic light scattering) can be used to deter-mine L. For a Gaussian distribution, exp [-(L-L) /2a ], eqn (12) can be wrriten as... 

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