Light microscopy (LM)

particle_characterization

Light microscopy (LM) is an alternative compendial technique to light obscuration for the analysis of subvisible particle in parenterals.

LM is listed in the pharmacopeias Ph. Eur. 2.9.19, USP <788> and USP <787>. For analysis, particles from at least 25 ml of sample are collected on a filter membrane and subsequently dried. The particles on the membrane are counted and sized under a microscope using 10- and 25-µm graticules. Particle counts are reported for the size classes ≥10 and ≥25 µm. Possibilities to improve the detection of proteinaceous particles captured on a filter are staining procedures, e.g., by Coomassie Blue or commercially available kits.

Light microscopy can be used as a viable option for batch release testing in cases that light obscuration [LO] is not feasible, e.g., due to high viscosity.

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