Quantitative Analysis of Silica in Silica-Kaolin Mixtures by Photoacoustic and Diffuse Reflectance Spectroscopies

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Abstract
The techniques of photoacoustic spectroscopy (PAS) and diffuse reflectance spectroscopy (DRS) are investigated for the quantification of silica using the IR bands at 1080,797,693, and 1875 cm−1. It is observed that, in both techniques, signal intensity increases linearly with mass initially. However, signal saturation sets in at much lower masses (>2 mg) in PAS than in DRS (>30 mg), showing that saturation is strongly technique dependent, in addition to having dependence on the absorptivity of the sample. These findings are applied to the quantification of silica in laboratory-generated silica-kaolin mixtures. It is shown that, with the use of the weaker band at 1875 cm−1 in DRS, satisfactory results for the quantification of silica are obtained.