It permitted the entire range of scattered intensities to be recorded on the film with a subsequent densitometer scan providing the relative scattered intensities. An interesting system based upon the use of high speed film was developed by Brunsting and Mullaney in 1974. Multiple detectors having different quantum efficiency have different response and hence needs to be normalized in this scheme.
Since the collection of data was made as the detector was placed at different locations on the arc, each position corresponding to a different scattering angle, the concept of placing a separate detector at each angular location of interest was well understood, though not implemented commercially until the late 1970s. Measurements were generally expressed as scattered intensities or scattered irradiance. The first commercial instrument (formally called a “scattered photometer”) was the Brice-Phoenix light scattering photometer introduced in the mid 1950s and followed by the Sofica photometer introduced in the late 1960s. Historically, such measurements were made using a single detector rotated in an arc about the illuminated sample. The measurement of scattered light from an illuminated sample forms the basis of the so-called classical light scattering measurement. The former framework is used for measuring aerosol particles while the latter was used to examine marine organisms such as phytoplankton. If single-particles scattering properties are to be measured, a means to introduce such particles one-at-a-time through the light beam at a point generally equidistant from the surrounding detectors must be provided.Īlthough most MALS-based measurements are performed in a plane containing a set of detectors usually equidistantly placed from a centrally located sample through which the illuminating beam passes, three-dimensional versions also have been developed wherein the detectors lie on the surface of a sphere with the sample controlled to pass through its center where it intersects the path of the incident light beam passing along a diameter of the sphere. Alternatively, cells incorporating means to permit measurement of flowing samples may be employed. Another required element is an optical cell to hold the sample being measured.
The insertion of the word “laser” was intended to reassure those used to making light scattering measurements with conventional light sources such as Hg-arc lamps that low angle measurements could now be made. Collimated light from a laser source is most often used, in which case the technique can be referred to as multiangle laser light scattering (MALLS). Multiangle light scattering (MALS) is a technique for determining, independently, the absolute molar mass and the average size of particles in solution, by detecting how they scatter light.
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