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Full Correction of Scattering Effects by Using the Radiative Transfer Theory for Improved Quantitative Analysis of Absorbing Species in Suspensions
Volume 67, Number 5 (May 2013) Page 526-535
RAIMUNDAS STEPONAVIČIUS and SURESH N. THENNADIL*
Sample-to-sample photon path length variations that arise due to multiple scattering can be removed by decoupling absorption and scattering effects by using the radiative transfer theory, with a suitable set of measurements. For samples where particles both scatter and absorb light, the extracted bulk absorption spectrum is not completely free from nonlinear particle effects, since it is related to the absorption cross-section of particles that changes nonlinearly with particle size and shape. For the quantitative analysis of absorbing-only (i.e., nonscattering) species present in a matrix that contains a particulate species that absorbs and scatters light, a method to eliminate particle effects completely is proposed here, which utilizes the particle size information contained in the bulk scattering coefficient extracted by using the Mie theory to carry out an additional correction step to remove particle effects from bulk absorption spectra. This should result in spectra that are equivalent to spectra collected with only the liquid species in the mixture. Such an approach has the potential to significantly reduce the number of calibration samples as well as improve calibration performance. The proposed method was tested with both simulated and experimental data from a four-component model system.
Index Headings: Scatter correction; Multivariate calibration; Near-infrared spectroscopy; Multiple light scattering; Radiative transfer equation; Adding–doubling method.