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Correcting the Relative Bias of Light Obscuration and Flow Imaging Particle Counters



Dean C. Ripple, Zhishang Hu


Purpose: Industry and regulatory bodies desire more accurate methods for counting and characterizing particles. Measurements of proteinaceous-particle concentrations by light obscuration and flow imaging can differ by factors of ten or more. Methods: We propose methods to correct the diameters reported by light obscuration and flow imaging instruments. For light obscuration, diameters were rescaled based on characterization of the refractive index of typical particles and a light scattering model for the extinction efficiency factor. For flow imaging, the method relied on calibration of the instrument with silica beads suspended in water-glycerol mixtures. Results: These methods were applied to four particle suspensions containing particles produced from heat stressed and agitated human serum albumin, agitated polyclonal immunoglobulin, and abraded ethylene tetrafluoroethylene polymer. Particle suspensions were measured by two flow imaging and one light obscuration apparatus. Prior to correction, results from the three instruments disagreed by a factor ranging from 4.6 to 48 in particle concentration over the size range from 2 µm to 20 µm. Bias corrections reduced the disagreement from an average factor of 14 down to an average factor of approximately 2. Conclusions: The methods presented show promise in reducing the relative bias between light obscuration and flow imaging.
Pharmaceutical Research


light obscuration, light scattering, flow imaging, flow microscopy, particle, particulate, protein


Ripple, D. and Hu, Z. (2015), Correcting the Relative Bias of Light Obscuration and Flow Imaging Particle Counters, Pharmaceutical Research, [online], (Accessed June 24, 2024)


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Created November 10, 2015, Updated November 10, 2018