Absorbance spectroscopy of light scattering samples placed inside an integrating sphere for wide dynamic range absorbance measurement.

Ayaka Mori,Eiji Tokunaga,Kyohei Yamashita,Yunosuke Tabata,Keisuke Seto

doi:10.1063/5.0066412

Ayaka Mori, Eiji Tokunaga + Show 3 more

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https://doi.org/10.1063/5.0066412

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Abstract

In the absorbance measurement of a sample that scatters light significantly, it is necessary to consider the effect of the attenuation of incident light due to scattering on the measured absorbance. Since the usual absorbance measurement with an integrating sphere (IS) cannot remove the influence of backscattering, we performed the absorbance measurement considering the light scattered to almost all solid angles by placing the sample inside the IS. Ni(NO3)2 and Co(NO3)2 aqueous solutions were used as non-scattering samples, and Ni(NO3)2 solutions mixed with submicrometer polystyrene spheres as scatterers were used as scattering samples. The sample-concentration dependence of the measured absorbance was investigated for the cell containing the sample placed at the entrance of or inside the IS. It was found that even inside the IS, the measured absorbance does not match the true absorbance because light is partially multiply transmitted through the sample or detected without being transmitted through the sample. Due to the latter reason, the saturated absorbance inside the IS was lower than that at the entrance. We derived the formula with three fitting parameters relating the measured and true absorbance taking these factors into account, which quantitatively reproduced the concentration dependence of the absorbance in the non-scattering sample. When the scattering samples were placed at the entrance and inside of the IS, the measured absorbance increased and decreased, respectively, compared to those without scatterers. This decrease in absorbance for the scattering samples inside the IS was also explained by the proposed formula slightly modified.

Highlights

Measuring the absorbance of a sample that scatters light is more difficult than measuring a sample that does not
In order to measure the true absorbance of the scattering sample taking into account the scattered light to all solid angles, the sample was placed inside the integrating sphere (IS) and the absorbance spectra were measured
The results showed, that the measured absorbance spectrum A′ does not match the true absorbance spectrum A due to the influence of “light that never passes through the sample” and

Summary

Introduction

Measuring the absorbance of a sample that scatters light is more difficult than measuring a sample that does not This is because the presence of scattered light gives an error to the measured absorbance.[1] it is important to know the absorbance of the light-scattering sample. The absorption spectrum of a phytoplankton suspension gives information such as the photosynthetic efficiency of the phytoplankton.[2] In addition, since the scattering of visible light by fine particles becomes pronounced when the particle size exceeds 100 nm, it is essential for optical characterization of such fine particles to evaluate the effect of scattering on the visible absorption spectrum of them.[1,3,4,5] The purpose of our study is to measure the exact absorbance of the samples that scatter light over the widest possible range of absorbance

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