Light Obscuration
Method Introduction
Light obscuration (LO) is listed in the pharmacopeias Ph. Eur. 2.9.19, USP <788>, USP <787> and USP<789>. During measurement, the sample is drawn into the system through a needle, and particles passing a laser beam block a certain amount of light and produce a “shadow” on a light-sensitive detector. The area of this shadow is then converted to an equivalent circular diameter of the particle based on a calibration curve generated with polystyrene standard beads.
LO allows the counting and sizing of subvisible particles in the size range from about 1 to 200 µm. The upper particle concentration limit is system-dependent, usually about 10^5 and 10^6 particles/mL. The pharmacopeias give specifications for particles >10 µm (less than 6,000 particles per container for low-volume parenterals of 100 mL or less) and particles >25 µm (less than 600 particles per container for low-volume parenterals of 100 mL or less). However, the quantification of smaller subvisible particles (>1 µm) is nowadays also expected by the regulatory authorities. At Coriolis, we have many years of experience using low-volume methods for the LO analysis of numerous biopharmaceutical products.
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Applications
The LO technique is used during all stages of development, from early research to batch release testing, to quantify subvisible particles. At Coriolis, LO can be offered in full GMP compliance.
The main advantages of light obscuration are the high sampling efficiency, as the whole sample volume can be analyzed during the measurement, and the short measurement and data handling times. However, the presence of air bubbles and the formation of Schlieren patterns can result in erroneously high particle levels in LO measurements. However, a well-established sample preparation procedure can avoid these issues. Like all light-based techniques, LO depends on a difference in refractive index between particle and solvent. The validity of LO results should thus be validated by using orthogonal methods.
Quality and Biosafety Level
We provide all our analytical services with the highest quality standards. Experienced scientists carry out each project, and a scientific reviewer comprehensively checks every report or data presentation.
We offer this technology with the following quality and biosafety levels:
Up to GMP Level
This method is available under GMP in dedicated labs with qualified equipment and full QA involvement.
Up to biosafety level 2
This method can be applied to nucleic acids, viruses, cells, viral vectors, including lentiviruses, and more.
Analytical Method Development, Qualification and Validation
For common sample types, we can often apply standardized methods with little setup effort. However, when needed, our experienced analytical experts create or optimize custom methods tailored to your active pharmaceutical ingredient, product type and development phase.
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