Raman spectroscopy and Zeta potential assay for the assessment of dissolved organic matter in natural waters

LEDESMA, ANA ESTELA; MEDINA AV; GOMEZ ROJAS, JORGE; HERRERA, E

Encuentro; LI Reunion Anual de la sociedad Argentina de Biofisica; 2023

The dissolved natural organic matter (NOM) plays a central role in aquatic environmentsand its composition determines how it reacts in the environment. A main process affectingNOM amount and composition in aquatic environments is biodegradation. That typicallyleads to the rapid loss of labile, low molecular weight aliphatic material, includingproteins, carbohydrates, and organic acids. However, it can also be accompanied by theproduction of high molecular weight aromatic material, such as fulvic and humic acids,through alteration of existing compounds and/or production of new compounds byheterotrophs.Raman spectroscopy is a powerful technique, which can be used in the study of complexmacromolecules in aqueous solution, owing to the weak Raman signal of water. Thisspectroscopy is an alternative inexpensive and rapid technique, moreover, requires noreagents, and allow identify the component present in NOM after treatment of naturalwater.The knowledge of particle size distribution and colloidal stability is very important for theirfunctioning in nature. The mobility of any particle is strongly affected by its size. Theaggregation of humic and fulvic particles can result in a loss of their mobility and in thedecrease of active sites accessible for pollutants in natural systems and theirbioavailability can be increased and decreased by the binding with those particles.Therefore, its charges play an important role for their binding.The study of organic matter in natural waters is hindered by its complex structure and lowconcentration. This work proposes the implementation of Raman spectroscopy and zetapotential for the identification and characterization of NOM. Raman spectra of watersamples from Icho Cruz River (31°28'30.4"S 64°35'30.7"W), are presented. Signal fromfulvic acid and humic substances were identified using standards and differenttreatments. The superficial charges present in the macromolecular aggregates indicatethe nature of the NOM component. Colloidal stability, indicated by more negative zetapotentials, was greater for water samples containing the humic acid fraction.These results demonstrated that this analytical technique serves as an alternative tool forNOM detection and offers advantages in terms of being fast, non-destructive, andrequiring little to no sample preparation.