Scattering techniques turbidimetry

The techniques that are able to perform the on-line evaluation of PSDs include fiberoptic dynamic light scattering (FODLS), turbidimetry, size fractionation techniques (such as capillary hydrodynamic fractionation chromatography, CHDF and field-flow fractionation. 

Turbidimetry and nephelometry are two related techniques in which an incident source of radiation is elastically scattered by a suspension of colloidal particles. In turbidimetry, the detector is placed in line with the radiation source, and the... 

Turbidimetry is ideally suited to detect the temperature at which a transparent polymer solution turns opaque. The temperature corresponding to the onset of the increase of the scattered light intensity is usually taken as the cloud-point temperature, TcP, although some authors define the cloud point as the temperature for which the transmittance is 80% (or 90%) of the initial value. This technique is commonly known as the cloud-point method [199]. Turbidimetry was employed, for instance, to show that the cloud-point temperature of aqueous PNIPAM solutions does not depend significantly on the molar mass of the polymer [150]. 

Another technique which is used to follow the extent of template polymerization vs. time is turbidimetry. Two types of measurements can be used here. The first is based on the determination of passed light intensity, the second on the determination of scattered light intensity. The former was used in many papers by Ferguson and co-workers for studies on polymerization of acrylic acid in aqueous solution in the presence of many homopolymers used as templates as well as for application of copolymers with interacting and non-interacting groups. This measurement was also used for studying com-... 

Light scattering is a physical phenomenon resulting from the interaction of light with particles in solution. Nephelometry and turbidimetry are analytical techniques used to measure scattered light. Light-scattering measurements have been applied to immunoassays of specific proteins and haptens. Specific applications are described in Chapters 9,20, and 26. 

FIGURE 26.5 Nephelometer. Light scattered by large molecules is measured at an angle a away from the axis of incident fight. The filters select the wavelength range desired and block undesired fluorescence. When a = 0, the technique is known as turbidimetry. 

Turbidimetric and nephelometric assay Nephelo-metry and turbidimetry, because of their speed and ease of use, are most widely used. These techniques can be used either by measuring the amount of Ag-Ab complex formation (endpoint methods) or by measuring the rate of complex formation (kinetic methods). The kinetic methods are more rapid because measurements are accomplished within 20 s, and are more precise because sample blanks are not necessary. Kinetic assays are, however, somewhat less sensitive because low-affinity antibodies do not have time to react. The occurrence of Ag-Ab formation is related to the amount of light scattering and is used as the basis for antigen quantification. This approach has been accompanied by the development of... 

Nephelometry is the measurement of turbidity by the direct evaluation of the degree of light scattering taking place in the medium. It is much more appropriate to media of lower turbidity in which the suspended particles are small. Turbidimetry and nephelometry can offer considerable time-saving advantages over gravimetric methods for the determination of particle concentrations, and are nondestructive techniques. 

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