engleski

Phase sensitive a.c. voltammetry as a simple, fast tracking tool for studying changes in the environment

Organic carbon (C) is an important component of many biogeochemical processes and can be a valuable indicator of environmental change [1]. The composition of organic matter (OM) in natural waters is complex, indeterminate, and variable over time. An important subset of dissolved and particulate organic C (DOC, POC) in the aquatic environment is OM with surface active properties, i.e., surface active substances (SAS) [1-3]. SAS are mainly produced autochthonously by biological activity (primary and secondary production, grazing), while part of SAS may also be introduced allochthonously (land and atmospheric input). SAS are the most reactive fraction of OM, which tend to adsorb at different phase boundaries and affect abiotic and biotic processes. Due to their strong adsorption properties, the presence of SAS in natural waters can be monitored by adsorption on the hydrophobic surface of the mercury (Hg) electrode using the electrochemical method of phase sensitive alternating current voltammetry (PSACV). PSACV can selectively measure faradic (in-phase signal) or capacitive current (out-of- phase signal) as a function of electrode potential. Out-of-phase measurements reflect the adsorption extent of all present SAS that take a part in adsorption on Hg in a competitive manner, expressed as the equivalent adsorption effect of a given amount (mg dm-3) of model SAS, usually the nonionic polyoxyethylene-t-octylphenol, Triton-X- 100 [1-3]. The signal depends not only on the concentration of SAS but also on its adsorption strength. Moreover, the type of OM present in the sample can be characterized by analyzes of the SAS desorption waves, which seem to be characteristic for the particular type of OM. Additional characterization is possible by normalizing SAS to the DOC content, giving normalized surfactant activity NSA = [SAS (eq. T-X-100) / DOC], which can be compared to the NSA of the selected model substances that are typical or expected for the samples (systems) studied [2, 3]. This study focuses on the changes in the quantity and quality of OM during the unusual phenomena in the northern Adriatic and rainfall event in central Croatia, as well as on a long-term study of OM in a eutrophic marine lake (Rogoznica lake) in the central Adriatic. Additionally, the effect of sample filtration will be presented, showing that the most reactive SAS pool belongs to the colloids, i.e. to the fraction < 0.22 um. ACKNOWLEDGMENTS This work is funded by the MARRES project, IP- 2018-01-1717.

voltammetry ; organic matter ; surface active substances ; extreme events

nije evidentirano