Light-scattering instrumentation principles

Fig. 10.4 The principle of low angle laser light scattering instruments.

In general, nephelometric measurements essentially require an instrument with a photocell placed in position so that it may receive selectively the scattered light rather than the transmitted light. As this principle and geometry also hold good specifically to fluorimeters and, therefore, these can be employed as nephelometers by selecting proper filters. 

The principles of absorptiometry have been applied to the measurement of turbidity. Suspensions of particles scatter incident radiation and, while there is no absorption of radiation by the analyte, the reduction in the transmitted radiation can be used as a measure of the degree of turbidity. Because absorption is not involved, there is no requirement for monochrornation but the fact that the extent of light scattering increases as the wavelength of the incident radiation decreases explains the fact that some instruments do incorporate a simple monochrornation system. 

Insitec now forms part of Malvern Instruments but is still based in California for process and laboratory R D. The EPCS are laser-based instruments for in-line particle measurements that provide information on particle volume concentration and size distribution. EPCS instruments are part of the larger group of electro-optical instruments (MALLS) whose principle of operation is based on light scattering from a group (or ensemble) of particles. Unlike other instruments operating on this principle, the EPCS can perform direct measurements of particle laden flow stream provided the concentration is within operating limits. 

For the micron size range an optical on-line particle sizer was used, working on the principle of white light scattering on single particles. This instrument provided number concentration and size distribution measurements in the range 0.3-30 pm, with a maximum of allowed particle number concentration of 10 particles/cm. ... 

Particle agglomerate sizes can be determined using a laser diffraction particle size analyzer, such as a Brinkmann PSA-2010. With this instrument, the principle of particle size measurement is based on various light scattering angles generated by paiTicles of... 

Plasma. In 1976 Montaser and Fassel introduced an AFS instrument in which EDLs were used for excitation and an ICP for atomization. Advantages of the plasma torch are good atomization efficiency and lack of chemical interferences. Interference due to light scatter is also minimal with a plasma atomizer. In principle, it is also possible to analyse solid samples by AFS by using a plasma atomizer. 

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