Injectable products must undergo a particulate count test to show they meet FDA requirements. USP <788> presents two different particle count test procedures – light obscuration and the microscopic particle count test. This post will focus on a visual illustration of the latter method.
There are two scenarios when the microscopic particle count test is used. One is when samples cannot be analyzed by light obscuration because they are hazy, have a high viscosity, or contain colloids and/or surfactants. The other scenario is when the average number of particles exceed the limit obtainable by the light obscuration method.
Particle counting by light microscopy has advantages. It allows you to capture the color and shape of the particle, which can be valuable information when trying to determine the root cause or the source of the particulate. In addition, if several particles are found during counting, you can perform a particulate analysis to identify the composition of the material. (Click here for a more detailed explanation on particulate analysis.)
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