Particle Size Determination in Semisolid Formulations

©2010 Particle Sciences, Inc. All rights reserved. centrifugation is a highly accurate technique, but it is not amenable to use with semisolid formulations with high viscosities. All the methods discussed so far may require dilution and while some drug product formulations can be diluted without changing the particle size distribution, others may be affected by dilution, which makes meaningful particle size measurement challenging. Optical microscopy, however, is a technique which lends itself quite naturally to the determination of particle size in situ. Particle sizing by optical microscopy and image analysis is a technologyintensive method requiring automated acquisition of photomicrographs. This is usually controlled by software that also handles the analysis of the images collected. The acquisition of a large number of image objects is required for statistically relevant measurements, which may include the determination of length, width, area, equivalent circle diameter, roughness, etc. With careful selection of objectives and camera, the technique has a broad dynamic range where the upper limit is several mm at low magnification and the lower limit is close to 1 μm, which is the minimum resolution achievable with the use of normal white light illumination. An advantage of microscopy over laser diffraction is the verifiable and calibrated acParticle Size Determination in Semisolid Formulations