Measuring the particle size of small quantities of dry powders using the Aero S and Mastersizer 3000

The routine measurement of particle size plays an important role in pharmaceutical and other industries, where it is often a critical-to-quality attribute for the product. Dispersion is critical for any particle size measurement and two principle routes are available in laser diffraction systems, wet and dry. If the powder is processed in a dry state and the end product is a dry powder, then a dry dispersion method is generally preferred. In the case of the pharmaceutical industry, active ingredients and excipients are generally handled dry during processing, and may be a dry powder in the final form for example in dry powder inhalers. In the early stages of product development, a pharmaceutical manufacturer may wish to measure the particle size of a sample of dry powder with less than 100mg of material in existence.

In this application note, we measure aliquots as small as 5mg of fine grade, pharmaceutical lactose and show that the measurement reproducibility is well within the ISO laser diffraction standard [1] guidelines on repeatability. This fine grade of lactose was chosen as both an established model material for active pharmaceutical ingredients and as a highly cohesive powder that is difficult to disperse.