engleski

Development of voltammetric method for characterization and determination of surface active natural organic matter (humic substances)

Dissolved organic matter (DOM) is an important constituent of all aquatic ecosystems. DOM is a heterogeneous system composed of various substances in a wide range of molecular weights with different properties, depending on their structure. Major fraction of DOM in aquatic environments consists of surface active chemical species. Surface active substances (SAS) are electro-inactive. However, the influence they have on the electrode double layer, during adsorption, enables their quantification. Further molecular characterisation can be derived through comparison with model compounds. In this type of research alternating current voltammetry (ACV) is commonly used technique [1]. During adsorption electrical double layer capacitance decreases, causing decrease in ac capacitive current. Square-wave voltammetry (SqW) and differential pulse voltammetry (DPV) methods are considered as insensitive to capacitive current. Applying these techniques for SAS measurements usually cause a sudden increase in adsorption and desorption current, due to sudden change in charge. This is seen as two peaks between which the current is very low, signifying the area of maximum adsorption [2]. Studying humic substances (HS) we noticed specific behavior while using SqW and DPV methods. While the ACV method shows characteristic current decrease, these methods show elevation of whole base current with respect to increase of HS concentration and/or accumulation time, without adsorption- desorption peaks. Additionally, we tested other compounds (proteins and polysaccharides) which showed characteristic adsorption-desorption peaks but no current elevation. This tells us it could be phenomenon effective only for HS and we propose its use for analytical purposes. The advantage of this method is possibility for simultaneously studying humic-SAS contribution with iodides or trace metal influence. The new procedure is currently tested on model solutions (IHSS fulvic and humic acid and XAD fractions) and real samples from the Krka River estuary. We are also testing it for assessment of copper complexing fractions. It was successfully applied on samples from 2017 (July and December). It is expected that new measurements would confirm its application as an alternative method for SAS measurements in natural samples. References 1. B. Ćosović, V. Vojvodić, Electroanalysis 22 (1998) 429-434 2. D. Jadreško, M. Zelić, Electroanalysis 27 (2015) 1669-1675.

Surface active substances ; Humic Sustances ; Voltammetry

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