BOOK OF ABSTRACTS 179 IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 Hall A Poster Session / Analysis and Characterization humic acid was capable of binding, on average, approximately 8 mM Cu²⁺. According to the synchronous correlation spectrum, the main change associated with increasing Cu²⁺ concentration was a decrease at 395 and 465 nm, while a slight increase was observed in the UV region. The asynchronous spectrum indicated that the change in the UV region preceded the decrease observed in the visible region. The infrared spectra allowed the identification of vibrations associated with humic acid functional groups at 1100, 1350, 1400, 1620, 1660 and 1720 cm⁻¹.In the synchronous correlation spectrum, the main changes were associated with these same wavenumbers. Based on the asynchronous spectrum, we established the following order: the carboxylate region (1400–1600 cm⁻¹) is dominant in copper binding, while the region between 850 and 1100 cm⁻¹ corresponds to structural rearrangement due to complex formation. Based on the heterospectral FTIR– fluorescence correlation, fluorescence quenching changes in parallel with the changes detected in the carboxyl/ phenolic and polysaccharide-like regions of the FTIR spectra. Our results demonstrate that Cu²⁺ binding affects several functional groups of humic acid, and that fluorescence quenching is a process coupled with structural changes. Keywords: humic acid; Cu²⁺; complex formation; synchronous fluorescence; FTIR; 2D-COS
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