IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 BOOK OF ABSTRACTS 38 Analysis and Characterization Monday, 24 August 2026 / Hall B+C SL13 Solid-Phase Fluorescence Excitation-Emission Matrix (SPF-EEM) Spectroscopy of Clay Mineral-Organic Matter Complex: Implications for the Origin of Soil Fluorescence Yuki Nakaya1, Maya Hosono1, Gakushi Yamaguchi2, Takashi Hirose1, Satoru Nakashima3, Nobuhide Fujitake4, Hiroshi Yamamura5, Hisashi Satoh1 1 Faculty of Engineering, Hokkaido University, North-13, West-8, Kita-ku, Sapporo, 060-8628, Japan. ynakaya@eng.hokudai.ac.jp 2 School of Engineering, Hokkaido University, North-13, West-8, Kita-ku, Sapporo, 060-8628, Japan 3 Research Institute for Natural Environment, Science and Technology (RINEST), #103 Purantsu-Ryokuchi, 3-19-20 Kasuga, Suita, Osaka 565-0853, Japan. 4 Graduate school of Agricultural Science, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe, 657-8501, Japan. 5 Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan. The authors are developing a nondestructive and non-extractive soil organic matter (SOM) analysis method by measuring solid-phase fluorescence excitation-emission matrix (SPFEEM) spectra [1-3]. In this study, clay mineral-organic matter complexes were prepared and their SPF-EEM spectra were measured in order to examine how organic matter adsorption on clay minerals affects EEM patterns. Three types of clay mineral, montmorillonite, kaolinite, and muscovite plate, were employed. BSA and amino acids were used as organic substances to be adsorbed. The clay mineral powder and organic substances were dispersed and dissolved in ultrapure water, adjusted to pH2.5, shaken for 72 hours, centrifuged, washed, and the precipitate was freeze-dried to obtain a clay mineral-organic matter complex [2,3]. A blank sample was obtained by the same treatment in a system in which organic substances are not dissolved. The amount of organic substances adsorbed on the clay was calculated by comparing total organic carbon (TOC) concentration of the supernatant at the time of centrifugation and the original TOC concentration before shaking. The muscovite was immersed in the organic aqueous solution adjusted to pH2.5 for 24 hours immediately after cleavage of both surfaces to obtain a complex. The surface structure was observed by atomic force microscopy (AFM). SPFEEM spectra were measured by NanoLog (HORIBA) [1-3]. In comparison with the blank sample, the montmorillonite-BSA complex showed a fluorescence maximum at Ex./
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