![]() Evaluation of the raw data was performed using non-parametric statistical methods and by taking into consideration the goodness-of-fit of the resulting model. For this purpose, the expected overlapping region of each red and blue scattering light patterns of the same particle size population was studied by measuring the particle size distribution of narrowly dispersed standards chosen across the 0.1 μm to 100 μm range. If so, the question remains as to how the internal algorithm combines and deconvolutes the signals when measurements are performed using both light sources and the blue light data are subtracted from the raw light energy signal. Since “a sequential combination of measurements with red and blue light sources” is employed to determine the particle size, it is reasonable to expect each channel (detector) will be populated by signals from both light sources. According to Mie Theory, diffraction light patterns vary depending on the refractive and absorption indices of the material and the medium as well as the wavelength of the light source interacting with the ensemble of particles, which would result in different signal intensities (diffraction patterns) identified by each detector. For the purpose of data collection, a series of 63 detectors is utilized. Given the aforementioned conditions, this work seeks to understand the relationship between the two light sources used in the determination of particle size distribution profiles despite the fact Mie Theory only considers one wavelength of light as part of its mathematical framework. Mie Theory is a rigorous solution for the scattering from a spherical, homogeneous, isotropic and non-magnetic particle of any diameter in a non-absorbing medium based on the known properties of a collimated, monochromatic light source.12 Derived from Maxwell’s Equations, Mie Theory also considers the refractive and absorption indices of the material and the medium. For a commonly used laser diffraction instrument in the pharmaceutical industry, the wide dynamic range is accomplished by using, “a sequential combination of measurements with red and blue light sources to measure across the entire particle size range … an advanced focal plane detector design able to resolve very small diffraction angles… and a powerful 10 mW solid state blue light source.” This wide range also is achieved using complex mathematical algorithms based on laser diffraction theory, such as Mie Theory. Because of this, constant improvements to analytical instrumentation based on the principles of laser diffraction theory are being made to improve its accuracy and precision, as well as its analytical range. A quick literature search results in hundreds of articles reporting on the applications of laser diffraction to measure particle size in natural sediments,1-3 combustion research4-6 and pharmacy.7-9 The versatility of the technique can be attributed to its capacity to analyze the diffracted light of an ensemble of particles, and its ability to perform measurements of wet and dry material dispersions,10,11 resulting in particle size characterization in a short period of time. ![]() The data are evaluated using non-parametric statistical methods and considering the goodness-of-fit of the results.ĭetermination of particle size distribution profiles by laser diffraction is a common analytical technique utilized across multiple industries. Of interest is the expected overlapping region of each light source scattering pattern of the same particle size, studied by measuring the particle size distribution of narrowly dispersed standards across the 0.300 μm to 100 μm range. This work is concerned with understanding how the instrument’s internal algorithms account for both red and blue light sources to accurately determine particle size distribution profiles. Mie Theory is a rigorous solution for the scattering from a spherical, homogeneous, isotropic and non-magnetic particle based on the properties of a collimated, monochromatic light source. The wide range of the instrument is also achieved using mathematical algorithms based on laser diffraction theory, such as Mie Theory. For a commonly used laser diffraction instrument, the wide dynamic range is accomplished by using a sequential combination of measurements with red and blue light sources. Due to its simplicity and precision, laser diffraction is an analytical technique frequently used in the determination of particle size distribution profiles.
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