In characterization of insoluble subvisible particulate matter in biopharmaceuticals, particles with sizes of 10 μm and larger are characterized by the light obscuration (LO) method as a test method in the Japanese and United States Pharmacopoeias (JP and USP). However, in recent years it has been reported that the LO method has poor sensitivity for highly transparent particles (e.g. aggregates of proteins) in comparison with the flow imaging (FI) method. As an additional limitation of LO, it is also impossible to predict the type of particle from the particle image in some cases.
This article introduces an example of characterization of the concentration of insoluble subvisible particles of micrometer-order size in a protein solution by using a Shimadzu iSpect DIA-10, which is based on the flow imaging method.