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Laser diffraction is a widely used particle sizing technique for materials ranging from hundreds of nanometers up to several millimeters in size. The main reasons for its success are:

  • Wide dynamic range - from submicron to the millimeter size range.
  • Rapid measurements - results generated in less than a minute.
  • Repeatability - large numbers of particles are sampled in each measurement.
  • Instant feedback - monitor and control the particle dispersion process.
  • High sample throughput - hundreds of measurements per day.
  • Calibration not necessary - easily verified using standard reference materials.
  • Well established technique - covered by ISO13320 (2009).

Principles

Laser diffraction measures particle size distributions by measuring the angular variation in intensity of light scattered as a laser beam passes through a dispersed particulate sample. Large particles scatter light at small angles relative to the laser beam and small particles scatter light at large angles, as illustrated below. The angular scattering intensity data is then analyzed to calculate the size of the particles responsible for creating the scattering pattern, using the Mie theory of light scattering. The particle size is reported as a volume equivalent sphere diameter.

Optical properties

Laser diffraction uses Mie theory of light scattering to calculate the particle size distribution, assuming a volume equivalent sphere model.

Mie theory requires knowledge of the optical properties (refractive index and imaginary component) of both the sample being measured, along with the refractive index of the dispersant. Usually the optical properties of the dispersant are relatively easy to find from published data, and many modern instruments will have in-built databases that include common dispersants. For samples where the optical properties are not known, the user can either measure them or estimate them using an iterative approach based upon the goodness of fit between the modeled data and the actual data collected for the sample.

A simplified approach is to use the Fraunhofer approximation, which does not require knowledge of the optical properties of the sample. This can provide accurate results for large particles. However it should be used with caution whenever working with samples which might have particles below 50µm or where the particles are relatively transparent.

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Expanding the capabilities of laser diffraction particle size analysis Webinar - Recorded (English)

The launch of the Mastersizer 2000 laser diffraction particle size analyzer in 1998 delivered advances in measurement automation (SOPs) and sample dispersion control which helped to move laser diffraction from being a research technique t...

Product:
Mastersizer 2000,Mastersizer 3000
Date recorded:
September 3 2014
Language:
English

Keywords: English Mastersizer 2000 Mastersizer 3000 Laser diffraction Webinar - Recorded Eastern Time 

Novel analytical technologies for product deformulation - Part 3 Webinar - Recorded (English)

Deformulation of oral solid dose (OSD) products requires generic companies to determine the physical and chemical properties of the excipients and active pharmaceutical ingredients (APIs) present within the reference listed drug product (...

Product:
Morphologi G3-ID
Date recorded:
September 2 2014
Language:
English

Keywords: English Laser diffraction Raman spectroscopy Webinar - Recorded Eastern Time Pharmaceutical development Drug discovery Pharmaceutical formulation and development Morphologi G3-ID 

Novel analytical technologies for product deformulation - Part 2 Webinar - Recorded (English)

The development of generic dry powder inhaler products represents a significant challenge to product developers due to the complex interactions which occur between the formulation, device and patient during drug delivery. Regulatory guidance ...

Product:
Morphologi G3-ID,Mastersizer 3000
Date recorded:
August 19 2014
Language:
English

Keywords: English Mastersizer 3000 Laser diffraction Raman spectroscopy Webinar - Recorded Eastern Time Drug discovery Pharmaceutical chemical development Pharmaceutical formulation and development Morphologi G3-ID 

The importance of particle size to spray hazard analysis Article (English)

Legislative changes concerning the safety and testing of spray products place increasing importance on fully understanding their characteristics and controlling the inhalation risks. Spray droplet size dictates how deeply a particle can p...


Keywords: Aerosols and sprays English Article Spraytec Laser diffraction Consumer products 

Masterclass 4: Configuring optical parameters for laser diffraction particle size analysis Webinar - Recorded (English)

Selecting the appropriate optical properties for particle size distribution measurement by laser diffraction can appear to be a difficult task, especially when characterizing unknown or mixed materials. In this webinar, we describe the av...

Product:
Mastersizer 3000
Date recorded:
June 19 2014
Language:
English

Keywords: English Mastersizer 3000 Particle size Laser diffraction Webinar - Recorded Eastern Time 
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