Concentration dependence of Kubelka–Munk function and apparent absorbance button sample holder infrared spectra

Abstract

Button sample holder infrared spectra in Kubelka–Munk function and apparent absorbance formats are evaluated. Trends in plots of vibration band area and peak intensity versus concentration are compared. Two test sample powders were comprised of different concentrations of caffeine dispersed in potassium chloride and copper thiosulfate mixed with kaolinite and potassium chloride in different ratios. When infrared spectra of caffeine and copper thiosulfate were measured by diffuse reflection, Kubelka–Munk calibration functions tended to be linear whereas apparent absorbance functions were curved. However, over narrow concentration ranges, both formats provided linear plots and exhibited similar sensitivities. For samples with the highest clay content, the kaolinite O–H stretching and inorganic oxide vibration band area versus concentration plots were linear over wider ranges than the Kubelka–Munk function plots.