Highlighted Services: USP 788 Microscopic Particle Count Test for Injectable Products

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Highlighted Services: USP 788 Microscopic Particle Count Test for Injectable Products

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.

The microscope is set up in a positive air pressure ISO 5 HEPA clean bench. It is equipped with reflected and transmission illumination.

Injectable solution containing visible particles.

Filter apparatus for filtering the injectable solution, in an ISO Class 5 clean bench.

For particle counting, a 1.0 micrometer polycarbonate filter is used.

The filtered sample is mounted on the microscope for particle counting. The microscope stage is set up for a systematic scan of the filter.

A particle counter allows you to keep track of two different particle sizes simultaneously.

The image on the left shows the graticule inside the ocular of the microscope. This ocular is made specifically for USP particle counting. Circles on the graticule are calibrated to 25 micrometers and 10 micrometers. Each division of the scale is 10 micrometers. This image was taken at 100X magnification.
The image on the right shows a field of view for particle counting. All the bright spots are particles. Particles greater than or equal to 10 micrometers, and particles greater than or equal to 25 micrometers, are counted.