Particle-size distribution and the concentration of polystyrene particles suspended in water were accurately recovered from the inversion of spectral extinction data measured with a commercial spectrophotometer. The instrument was modified by placing a spatial filter in the collection optics to prevent low-angle scattered light from affecting the measurement of transmitted power. The data were inverted by use of a nonlinear iterative algorithm. When the extinction coefficient is measured in the λ range of 0.3–1.1 µm, the particle distributions can be retrieved over a diameter range of 0.6–2.8 µm for a wide interval of sample concentrations. The average diameters are recovered with a precision of better than ±1% and with accuracies consistent with the uncertainties by which the nominal diameters are known. The relative standard deviations of distributions corresponding to monodisperse samples are ±5–10%, whereas the accuracy on the measured concentrations is ∼5%.
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