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A method to correct for spectral variations in multiwavelength responses using a photon time-of-flight measurement was investigated. A new approach is described where near-infrared spectra of various absorbing
and scattering solutions are corrected for nonlinear variations in the measured attenuation. The spectral attenuation measured in a sample is related to the concentration of the analyte as well as the scattering
from the medium. The dependence of the detected attenuation on the absorption and scattering at a single wavelength can be described by the steady-state diffusion approximation. With the use of the steady-state
diffusion approximation, single-wavelength correction methodologies for multiwavelength responses were developed to refine constituent estimates in a scattering medium. The single-wavelength corrections
examined the use of multiwavelength responses ratioed to the absorption and scattering determined at a single wavelength to reduce the scattering influence in the detected attenuations. The single-wavelength
correction method improved constituent estimates in a variable medium. The correction utilized the absorption and scattering determined from processed time-resolved photon distributions at a single wavelength.
Partial least-squares (PLS) regression was used to obtain constituent absorption estimates from diffuse transmittance spectra of turbid samples. A 70% improvement over PLS-processed spectra was obtained
with a combined single-wavelength absorption and scattering correction. In comparison to steady-state multiwavelength correction methods such as wavelength normalization, derivative spectroscopy, and multiplicative
signal correction, the results demonstrate a significant improvement in estimates of the dye concentration. Results suggest a practical method to correct for scatter variations in multiwavelength responses
for routine spectroscopic chemical analysis of turbid samples.
The Society publishes the internationally recognized, peer reviewed journal, Applied Spectroscopy, which is available both in print and online. Subscriptions are included with membership or can be purchased by institutional or corporate organizations. Abstracts may be viewed free of charge. Previously published as Bulletin (Society for Applied Spectroscopy)