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.
Measuring a fine grade of lactose
Aliquots of lactose were weighed out and handled with care to avoid powder compaction or adhesion to the weigh boat. An aliquot of 5mg was chosen as this allows for 20 measurements from the available 100mg, providing sufficient aliquots for both method development and reproducibility testing.
Reproducibility in 5mg aliquots
Six aliquots of the fine grade lactose were prepared and dispersed using the Aero S. A typical particle size distribution is shown in figure 1. The variation in the results, or reproducibility, was less than 0.8% for Dv (50) (table 1A). The ISO standard [1] states that the variation between repeated measurements (RSD %) should be less than 3% for Dv (50). As fine lactose is a particularly cohesive material achieving such low variation between measurements illustrates the excellent dispersion performance of the Aero S.
Download the full Application Note as PDF
Newsletters
Receive the latest analytical scientist news, personalities, education, and career development – weekly to your inbox.
