Determination of Particle Mixture Composition by Visible Spectroscopy

Limited methods exist to determine the composition of particle mixtures. This research presents a simple UV-vis-spectroscopy-based method for the separate quantification of particles mixtures considering the following: synthesized ferrihydrite, commercial Fe<inf>2</inf>O<inf>3</inf>, and natural allophane. Calibration curves and adsorption/scattering coefficients are determined for each particle at different wavelengths. This is the main input to solve equation systems and, ultimately, quantify particle concentration in binary mixtures. The limit of detection varies with wavelength and particle type, yielding values as low as 1.5, 0.2, and 1.6 mg L−1 for ferrihydrite (500 nm), Fe<inf>2</inf>O<inf>3</inf> (450 nm), and natural allophane (450 nm), respectively. This study provides a simple, low-cost and straightforward method, compared to atomic-spectroscopy- or chromatography-based techniques, for resolving the composition of binary particle mixtures in suspension. © 2025 by the authors.