Laser Diffraction – Unlimited?

Abstract

Within the past 20 years, particle size analysis with laser diffraction (LD) has been subject to rapid development, extending the size range stepwise from 1-200~m to about 0.1-3500 pm. The limits of LD are discussed in terms of light sources, the influence of the beam diameter, special Fourier optics and a new detector design. It is shown that the size range is not only restricted by the wavelength of the laser and the transmission limits of the medium. Its extension is mainly related to improvements in the measurement of the angular intensity distribution. Influences from stability and flow dominate on the coarse side of the measuring range. On the fine side, the spatial extension of aerosols and the resulting demand for extended working distances can be covered only in a parallel laser beam. Extended Fourier optics in combination with an adaptable beam expansion technique and a detector with virtual borders between

Particle engineering: A strategy for establishing drug substance physical property specifications during small molecule development

“…Two schools of thought have developed around this topic: one is to try to understand the impact of particle shape on laser diffraction measurements, while the other is to select alternate particle sizing techniques that are better equipped to deal with both particle size and shape. Investigators have proposed that it is possible to deconvolute the particle size and shape information obtained by laser diffraction 7–9, 24, 25. This is a daunting task considering the computer codes used for laser diffraction instruments are proprietary, a variety of light sources and detector arrays are used to gather the scattered light, and no single solution exists for all instruments.…”

Laser Diffraction Spectroscopy: Influence of Particle Shape and a Shape Adaptation Technique

“…a(x) lateral axis of an ellipse with the same area as a projected sphere with diameter x aðxÞ lateral axis of an ellipsoid with the same volume as a sphere with diameter x b(x) longitudinal axis of an ellipse with the same area as a projected sphere with diameter x E(U,V) electromagnetic field function f focal length p(u,v) object function I intensity J 1 Bessel function k wavenumber m refractive index q 0 =q 3 number/volume distribution x particle diameter ␤ spherical polar coordinate of the ellipsoid rotation (latitude angle) spherical polar coordinate of the ellipsoid rotation (longitude angle) F spherical polar coordinate of the diffraction pattern l wavelength of light axis ratio of an ellipsê axis ratio of an ellipsoid scattering angle, spherical polar coordinate of the diffraction pattern 9 References…”

“…Considering the variety of optical measurement techniques available, laser diffraction spectroscopy is distinguished by its wide range of application, simple optical set-up and uncomplicated handling [1]. The principle of measurement is based on the diffraction of laser light by the particle assembly dispersed in a gas or a liquid (see Figure 1) and the measurement data obtained are evaluated by applying the Fraunhofer diffraction theory.…”

Influence of the Storage Orientation on the Aerodynamic Particle Size of a Suspension Metered Dose Inhaler Containing Propellant HFA-227

“…This methodology, which is described in the literature, [24][25][26] provides a combined distribution of the droplets associated with the drug as well as the droplets that are not associated with drug (i.e., contain propellant alone or with other nonvolatile ingredients).…”

“…A special adapter for which MDI actuation could be performed automatically was attached. According to this method, [24][25][26] a detector with 31 channels is used to measure the diffraction pattern caused by the presence of particles in the path of the laser beam. The measurement begins after the first few spray droplets pass through the laser beam and stops when the spray decays below a detectable level.…”