IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 BOOK OF ABSTRACTS 178 Poster Session / Analysis and Characterization Hall A P1.1 Investigation of Humic AcidCopper(II) Complex Formation Petra Csicsor-Kulcsár1, Erzsébet Szabó-Bárdos1, Ottó Horváth1, Attila Csicsor2, János Csicsor2 1 Research Group of Environmental and Inorganic Photochemistry, Center for Natural Sciences, University of Pannonia, Veszprém, Hungary. kulcsar.petra23@gmail.com 2 Hymato Products Kft., Balatonfűzfő, Hungary In natural waters, the speciation of trace elements and heavy metals—and consequently their transport, mobility and ecotoxicological impact—is largely controlled by dissolved organic matter (DOM). Through complex formation and colloidal stabilization, DOM can alter the ratio between “free” and bound metal fractions. Complex formation is often accompanied by subtle functional-group transformations and conformational or matrix-related structural rearrangements. For the quantitative and structural interpretation of this process, the integrated evaluation of several spectroscopic perspectives, including UV–Vis, fluorescence and FTIR spectroscopy, is highly justified. Heterospectral two-dimensional correlation methods are particularly useful in this respect, as they support the separation of overlapping signals and help reveal the sequence of spectral changes. The aim of this work was to characterize the interaction between humic acid and copper(II) in aqueous medium using absorbance, synchronous fluorescence and FTIR measurements, combined with two-dimensional correlation spectroscopy (2D-COS). Humic acid samples were titrated with CuCl₂, followed by a 24-hour equilibration period, after which part of the samples was filtered. Absorbance and synchronous fluorescence spectra were recorded for both filtered and unfiltered fractions. The remaining samples were lyophilized and subsequently analyzed by FTIR spectroscopy. At low Cu²⁺ concentrations, the absorbance spectra showed increasing absorbance and shoulder formation, whereas at higher concentrations changes in the shape and decrease of the spectra indicated precipitation. Based on the differential logarithmic absorbance spectra, the main changes were associated with the 240–280 nm and 325–375 nm regions, suggesting the dominant role of carboxylate and phenolic binding sites. In the synchronous fluorescence spectra, concentration-dependent quenching of the humic-like regions at approximately 395 and 465 nm was observed. In the filtered samples, a new peak appeared at around 300 nm. Based on CuCl2 calibration and the filtered samples, it was established that 25 mg/L
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