Laser diffraction

Introduction

Laser diffraction is used for determination of particle size distribution. Determination of particle size distribution and understanding how it affects your products and processes can be critical to the success of drug development, as it has large impact on reactivity, dissolution rate, flowability etc. The particle size distribution measured by laser diffraction can further be used for:

  1. Detection of batch to batch variations
  2. Test the influence of production changes on the particles
  3. Detection of agglomerates

The method complies with Ph. Eur. 2.9.31

Instrument and measuring principle

By laser diffraction analysis it is possible to measure particles sizes between 0.02 and 2000 µm. The sample is dispersed in either air or a suitable liquid media. The laser passes through the dispersion media and is diffracted by the particles. The diffraction light pattern (He-Ne laser) is dependent on the particle size (read about laser diffraction theory ). The laser diffraction pattern is measured and correlated to the particle size distribution based on Fraunhofer or Mie theory. The use of Mie theory presupposes knowledge of the light refractive index of the particles and the dispersion media and the imaginary part of the refractive index of the particles. Particle Analytical can determine these refractive index parameters.

The laser diffraction instrument applied by Particle Analytical (Malvern Mastersizer 2000 and 3000) has a flow-through cell for dispersion of particles in liquid media or a dry dispenser for dispersion of particles in air. Wet dispersion presupposes that the particles are insoluble in the liquid. Therefore method development is required. We typically offer either a simple non-GMP suitability screening or a full length GMP method development.

Technical info  
Instruments Malvern Mastersizer 2000
Dispersion units Hydro2000SM, Hydro2000S and Scirocco2000 from Malvern
Dispersion media Liquid or air
Parameters Sonication, stirring speed (liquid) feeding rate, pressure (air)
Measuring range 0.02- 2000 µm (liquid) 0.1-2000 µm (air)
Sample amount 10-500 mg (liquid) 0.5-10 g (air)

A typical result from a laser diffraction measurement.