Large scale isolation—in gram quantities—of dissolved organic matter (DOM) from natural waters is necessary for detailed investigation of its role in chemical and microbial processes driving carbon cycling under conditions of global climate change. The best candidate for a use in these large-scale experiments is a bulk sorbent Bondesil PPL, which has the same modification as the widely used Bond Elut PPL sorbent. There have been no studies so far reported on interchangeability of these sorbents with regard to DOM isolation. This work was devoted to comparative studies on sorption efficiency and molecular selectivity of these two sorbents—Bond Elut PPL and Bondesil PPL with regard to DOM components. Fulvic acids (FA) from peat water leachate were used as a model DOM. Laboratory solid phase extraction (SPE) setup was used for monitoring sorption recovery and extraction yield. It included three parallel experiments on pre-packed Bond Elut PPL cartridges (500 mg/3 mL) and three self-packed Bondesil PPL cartridges (500 mg/3 mL). Fourier transform ion cyclotron resonance mass spectrometry (FT ICR MS) and 13C/1H nuclear magnetic resonance (NMR) spectroscopy were used for determination of molecular and structural group compositions of the FA isolates obtained with a use of two different sorbents. The results of this study allowed a conclusion on interchangeability of the two sorbents used in this study for the purposes of DOM isolation from natural waters. This conclusion was backed up by similarity of sorption behavior of the peat FA components on both sorbents and by high similarity of molecular compositions and carbon distribution among the main structural groups.

Redox moieties, which are present in the molecular backbone of humic substances (HS), govern their antioxidant properties. We hypothesized that a directed modification of the humic backbone via incorporation of redox moieties with known redox properties might provide an efficient tool for tuning up antioxidant properties of HS. In this work, hydroquinonoid and hydronaphthoquinonoid centres were used, which possess very different redox characteristics. They were incorporated into the structure of coal (leonardite) humic acids CHA) and peat fulvic acids (PFA). For this goal, an oxidative copolymerization of phenols was used. The latter was induced via oxidation of hydroquinones and hydroxynapjtaquinones with a use of Fenton’s reagent. The structure of the obtained products was characterized using NMR and FTIR spectroscopy. H/D labelling coupled to FT ICR mass spectrometry analysis was applied for identification of the reaction products as a tool for surmising on reaction mechanism. It was shown that covalent -C-C- bond were formed between the incorporated redox centers and aromatic core of HS. The parent humic acids and their naphthoquinonoid derivatives have demonstrated high accepting capacity. At the same time, fulvic acids and their hydroquinonoid derivatives have possessed both high donor and high antioxidant capacities. The kinetic studies have demonstrated that both humic acids and their derivatives showed much slower kinetics of antioxidant reactions as compared to fulvic acids. The obtained results show, firstly, substantial difference in redox and antioxidant properties of the humic and fulvic acids, and, secondly, they can serve as an experimental evidence that directed chemical modification of humic substances can be used to tune and control antioxidant properties of natural HS.

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