Light Obscuration (LO) / Single Particle Optical Sensing (SPOS) Technology

Light obscuration (LO) or Single particle optical sensing (SPOS) is a high-resolution analysis technique which is widely accepted by numerous standards and guidance agencies such as ISO, USP, and ASTM as an appropriate method for measuring the size and number of subvisible particles injectable suspensions, ophthalmic solutions, industrial oils and slurries, and even dilute waste/process water. In addition, it is the technique of choice for USP Particulate Matter analysis per USP 729, 787, 788, and 789. It can also be used to obtain an overall size distribution when using a light obscuration particle counter. Light obscuration works by passing a dilute stream of particles in a liquid suspension between a light source and a detector. The light source is a laser diode, which illuminates individual particles in the stream to generate a shadow or blockage of light on the detector. The detector measures the reduction in light intensity and employing a calibration curve, processes the signal to determine particle size.