Comparison of Beer's Law and Thermal Lens Techniques for Absorption Measurements under Conditions of High Scattering Backgrounds

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Abstract
Thermal lens spectroscopy has been experimentally compared to the conventional Beer's law method in situations where the sample under study possesses substantial light-scattering properties. Large errors in the measured absorbance were found with the conventional transmission-based approach. However, the thermal lens method was found to provide significant experimental immunity from the effect of light scattering on the measurement process. Both the absorbance and light-scattering properties of the samples tested were varied over a range in excess of an order of magnitude. The thermal lens method provided absorbance values for all samples tested which were as good as those obtained for samples that did not possess scattering characteristics. The results demonstrate that the immunity from light-scattering perturbations is substantial, thereby eliminating the need to match the scattering properties of standards and unknowns for accurate quantitation. The experimental results are compared to theoretical predictions and found to be in good agreement.