Optimization Of Dry Powder Particle Size Analysis

By Mark Bumiller
Vice President of Particle Products
HORIBA Instruments

Laser diffraction (LD) has established itself as a leading method for particle size analysis in a wide range of applications, thanks to its speed, reproducibility, accuracy, and ease of use. This technique measures light scattered from a particle surface, the angle of which depends primarily on the size of the individual particles. A typical LD system design includes a light source (or light sources), a measurement cell, and an array of detectors to measure the intensity of light over the angular range. The general principles behind this technique have been covered in detail in a number of documents.

The earliest particle size analyzers (PSAs) based on LD had limited measurement range, resolution, and flexibility. Historically, the sample has been presented to the measurement zone in a fluid dispersion. This approach has the widest range of applicability for suspensions, emulsions, and dry powder samples that can be analyzed as dispersions. Dispersion in a fluid also allows the use of alternate fluids that can wet the particle surface, surfactants to aid in dispersion, and mechanical energy such as ultrasonic treatment to disperse agglomerates. With the ongoing development of measurement optics and algorithms, the size range has been extended on current systems to measure 0.01 to 3,000 µm.