Laser Diffraction Particle Size Analyzer

The Beckman Coulter LS 13 320 particle size analyzer measures the size distribution of particles suspended either in a liquid or in dry powder form by using the principles of dynamic light scattering (DLS). Specifically, the instrument measures the intensity (I) of light scattered by the particles as a function of the scattering angle (). In order to compute the size distribution, the composite scattering pattern I() is deconvolved into a set of individual number, one for each size classification, and the relative amplitude of each number is a measure of the relative volume of equivalent spherical particles of that size. This deconvolution provides particle size distribution I(d) based on either the Fraunhofer or Mie theories. The LS 13 320 optical system is comprised of a monochromatic source of illumination (a 5 mW laser diode with a wavelength of 750 nm and a secondary tungsten-halogen light source for the PIDS detector system), a sample chamber in which the sample interacts with the illuminating beam, a Fourier lens system used to focus the scattered light, and an array of photodetectors to record the scattered light intensity patterns. The instrument has three sets of detectors (one for the low-angle scattering, the second for mid-angle scattering, and the third for high angle scattering) and incorporates also a PIDS (Polarization Intensity Differential Scattering) detector to provide size distribution in a wide size range from 40 nm to 2000 µm. Analysis can be performed either in water or in organic solvents as particle suspending liquid. The technique can be applied to a wide range of materials (metals, polymers, ceramics and proteins) and has a relevant role in several research fields, including the biomedical, food and environmental fields.