Light scattering instruments

Figure 10.9 Light-scattering photometers, (a) Schematic top view showing movable photodetector. (Reprinted from Ref. 2, p. 176.) (b) Cutaway photograph of commercial light-scattering instrument, the Brice-Phoenix Universal Scattering Photometer. (Photo courtesy of the Virtis Co., Gardiner, New York.)...

Nephelometer an instrument that measures the amount of light scattered. 

The most widely used molecular weight characterization method has been GPC, which separates compounds based on hydrodynamic volume. State-of-the-art GPC instruments are equipped with a concentration detector (e.g., differential refractometer, UV, and/or IR) in combination with viscosity or light scattering. A viscosity detector provides in-line solution viscosity data at each elution volume, which in combination with a concentration measurement can be converted to specific viscosity. Since the polymer concentration at each elution volume is quite dilute, the specific viscosity is considered a reasonable approximation for the dilute solution s intrinsic viscosity. The plot of log[r]]M versus elution volume (where [) ] is the intrinsic viscosity) provides a universal calibration curve from which absolute molecular weights of a variety of polymers can be obtained. Unfortunately, many reported analyses for phenolic oligomers and resins are simply based on polystyrene standards and only provide relative molecular weights instead of absolute numbers. 

Dynamic light scattering (DLS) Translational diffusion coefficient, hydrodynamic or Stokes radius branching information (when Rh used with Rg) Fixed 90° angle instruments not suitable for polysaccharides. Multi-angle instrument necessary. [3]... 

Seligson s group (95) has published a similar turbidimetric procedure but used nephelometry to measure continuously the effect of lipase on the light scattering of an olive oil emulsion. The instrumentation and approach is the same as that described above for the nephelometric determination of amylase. The method according to the authors is fast and precise with good specificity and sensitivity. The short time required for analysis makes it suitable for emergency use. The technical simplicity permits this method to be easily automated, and it appears to be the lipase method of choice. 

With the development of new instrumental techniques, much new information on the size and shape of aqueous micelles has become available. The inceptive description of the micelle as a spherical agglomerate of 20-100 monomers, 12-30 in radius (JJ, with a liquid hydrocarbon interior, has been considerably refined in recent years by spectroscopic (e.g. nmr, fluorescence decay, quasielastic light-scattering), hydrodynamic (e.g. viscometry, centrifugation) and classical light-scattering and osmometry studies. From these investigations have developed plausible descriptions of the thermodynamic and kinetic states of micellar micro-environments, as well as an appreciation of the plurality of micelle size and shape. 

Branching in the polymer chain affects the relationship between retention and molecular weight.83 Universal calibration has been used with some success in branched polymers, but there are also pitfalls. Viscosimetry84-91 and other instrumental methods have proved to be useful. A computer simulation of the effects of branching on hydrodynamic volume and the detailed effects observable in GPC is available in the literature.92 93 In copolymer analysis, retention may be different for block and random copolymers, so universal calibration may be difficult. However, a UV-VIS detector, followed by a low-angle light-scattering (LALLS) detector and a differential... 

Billiani, J., Amtmann, I., Mayr, T., and Lederer, K., Calibration of separation and instrumental peak broadening in SEC coupled with light-scattering of simple polymers,. Liq. Chromatogr., 13, 2973, 1990. 

The lifetime detection techniques are self-referenced in a sense that fluorescence decay is one of the characteristics of the emitter and of its environment and does not depend upon its concentration. Moreover, the results are not sensitive to optical parameters of the instrument, so that the attenuation of the signal in the optical path does not distort it. The light scattering produces also much lesser problems, since the scattered light decays on a very fast time scale and does not interfere with fluorescence decay observed at longer times. 

---