Absorbance Measurement of a Scattering Sample Placed Inside an Integrating Sphere and Analysis by Monte Carlo Simulation

Absorption measurements of scattering samples overestimate the absorption because the transmitted light is attenuated by scattering. In order to avoid this, we placed a sample inside an integrating sphere (IS) and performed absorption spectroscopy. The absorbance measured by this method is non-linear with respect to the absorption coefficient of the sample because light can take different paths IS inside the sample. Therefore, we attempted to estimate the relationship between the absorption coefficient and the measured absorbance by simulating the behavior of photons inside the IS and sample by Monte Carlo simulation(MC method). Using an aqueous nickel nitrate solution which is a non-scattering sample and a scattering sample prepared by mixing an aqueous nickel nitrate solution and polystyrene beads, it was verified whether the measurement and the simulation results agree with each other. As a result, in the scattering sample, the measurement results could be reproduced by the MC method, while in the adjusted scattering sample, a discrepancy was observed between the simulation and the measurement results in the high absorption region. From the DLVO theory, this can be explained to be caused by particle aggregation at high concentrations because the aqueous nickel nitrate solution is an electrolyte solution.