Light scattering corrections

Next let us consider the light scattered by liquids of low molecular weight compounds. We are actually not directly interested in this quantity per se, but in scattering by solutions-polymer solutions eventually, but for now solutions of small solute molecules. The solvent in such a solution does scatter, but, in practice, the intensity of light scattered by pure solvent is measured and subtracted as a blank correction from the scattering by the solution. 

The latest trend is to smaller beads in smaller columns, as this saves eluent and shortens the time for a chromatographic analysis. This argument can be correct if only one suitable detector is used. However, these modern small columns are not optimal for a combination of detectors. So-called multiple detection is a combination of some detectors with different measurement principles (differential refractometer, spectral photometer, light-scattering detector, on-line viscometer) behind the last column, mostly in series, seldom in a branched ( parallel ) order. In this way, the tedious preparative fractionation of a polymer sample can often be avoided. 

In the previous section it has been shown that the measured sample absorbance may be higher than the true absorbance signal of the analyte to be determined. This elevated absorbance value can occur by molecular absorption or by light scattering. There are three techniques that can be used for background correction the deuterium arc the Zeeman effect and the Smith-Hieftje system. 

This stipulation of the interaction parameter to be equal to 0.5 at the theta temperature is found to hold with values of Xh and Xs equal to 0.5 - x < 2.7 x lO-s, and this value tends to decrease with increasing temperature. The values of = 308.6 K were found from the temperature dependence of the interaction parameter for gelatin B. Naturally, determination of the correct theta temperature of a chosen polymer/solvent system has a great physic-chemical importance for polymer solutions thermodynamically. It is quite well known that the second viiial coefficient can also be evaluated from osmometry and light scattering measurements which consequently exhibits temperature dependence, finally yielding the theta temperature for the system under study. However, the evaluation of second virial... 

Apart from their utility in determining the correction factor 1/P( ), light-scattering dissymmetry measurements afford a measure of the dimensions of the randomly coiled polymer molecule in dilute solution. Thus the above analysis of measurements made at different angles yields the important ratio from which the root-mean-square... 

Turbidity as determined by light-scattering measurements, and the same quantity corrected for dissymmetry (Chap. VII). 

The parameter c can be easily determined by using viscometric measurements, which yield a relative number, or by performing, for example, light scattering measurements, which yield absolute values of c. Viscometric measurements are most commonly used because results are obtained quickly. However, this relative method is not equivalent to the absolute value of c LS and only absolute determination methods such as light scattering result in correct values of c. ... 

Light scattering by the sample can cause correctable (14) errors in photoacoustic spectra, particularly at visible amJ shorter wavelengths. However, at mid-infrared wavelengths this is no longer an Important consideration. 

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