Internal interference

If the scattering molecules are not isotropic, we must make corrections. The correction factor for anisotropy involves the deporalization ratio which is defined as the ratio of the horizontal to the vertical components of the scattered light at a 90° angle when the incident hght is unpolarized. The correction factor is (6 - 7P )/(6 + 6P ) for and (3 - 7P )/(6 + 7P ) for T900. 

FIGURE 14.3 Scattering envelopes —, symmetrical, no destructive interference —, scattering envelope, nonsymmetrical, with destructive interference. 

The term 4ti is the sum of all possible orientations that can be obtained from 

The amplitude A (i.e., OA) is related to the phase shift 4 , our major interest here, between scattered points (O and B). Their average values are related in the form 

This result shows that the average amplitude scattered by a rotating molecule exhibits g- (or 0) and r-dependent minima and maxima which could possibly be used to determine the internuclear distance r. 

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This internal interference is described by the particle form factor, P. It allows the direct calculation of the radius of gyration, of the macromolecules... 

The optical constant K is a function of the refractive index and the refractive index increment, and P (0) is the particle scattering function which depends on internal interference. This function is influenced by the particle shape and is less than 1 for molecules large compared with... 

Mixtures of beta-particle-emitting nuclides of more than one element usually have overlapping spectra. This is also often true for alpha-particle-emitting nuclides. Some of these mixtures can be analyzed by ICP-MS without internal interferences. For example, the alpha-particle spectra of " Np and Pu partially overlap even under the best of conditions, whereas ICP-MS is appropriate for analysing the long-lived... 

For an ideal solution of small particles, KcjRe, where c is the polymer concentration and is a system constant depending only on the solvent and 9, becomes the reciprocal of the weight-average molecular weight. For non-ideal solutions, molecular properties are expanded as a power series in concentration. Corrections can also be made for complications that arise when the size of the polymer becomes comparable to the wavelength of the light used (internal interference). 

Bacteria are usually large nonspherical particles. Internal interference effects can be very important. Recent work shows that qt scaling should not occur in these cases. In this event it will be difficult to determine the speed distribution from interference fluctuations (see Berne and Nossal, 1974). 

Assume that all particles present are of such a size that no internal interference occurs. Use the equations given in Problem 10.14. 

For solutions of macroiiiolecules, whose size is commensurablo with A, internal interference contributes to the scattering asymmetry as well. Then (Debye et al., 1962b)... 

FIGURE 14.9 External interference as shown in the Zimm plot. In these cases, there is not only internal interference but also external interference in light scattering. So far there is no simple theory to treat external interference in light scattering. 

High resolution mass spectrometry offers high selectivity for the analysis of PCTs and toxaphene congeners in environmental and biological samples and avoids the specific internal interferences and the effect of environmental matrices. Both HRGC El MS and HRGC-ECNTMS in the SIM mode can be used as... 

Fig. 3.13 Schematic illustration of the origin of internal interference during light scattering from a polymer molecule in solution. The light scattered from different parts of the molecule arrives out of phase at point P. 

The scattering Equation (3.90) which was calculated previously can be modified to include the effect of internal interference and becomes... 

It is not always desirable to eliminate internal interference as it can be used to advantage to obtain information concerning the conformations of the polymer coils. It is possible theoretically to calculate P 6) as a function of the size and shape of the coil. Such calculations are beyond the scope of this book and it will suffice to say that it can be shown that for a random Gaussian coil when 6 is small... 

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