Asymmetrical Flow Field-Flow Fractionation Methods for Quantitative Determination and Size Characterization of Thiols and for Mercury Size Speciation Analysis in Organic Matter-Rich Natural Waters

Abstract

Asymmetrical flow field-flow fractionation (AF4) efficiently separates various macromolecules and nano-components of natural waters according to their hydrodynamic sizes. The online coupling of AF4 with fluorescence (Fluo) and UV absorbance (UV) detectors (FluoD and UVD, respectively) and inductively coupled plasma–mass spectrometry (ICP-MS) provides multidimensional information. This makes it a powerful tool to characterize and quantify the size distributions of organic and inorganic nano-sized components and their interaction with trace metals. In this study, we developed a method combining thiol labeling by monobromo(trimethylammonio)bimane bromide (qBBr) with AF4–FluoD to determine the size distribution and the quantities of thiols in the macromolecular dissolved organic matter (DOM) present in highly colored DOM-rich water sampled from Shuya River and Lake Onego, Russia. We found that the qBBr-labeled components of DOM (qB-DOM) were of humic type, characterized by a low hydrodynamic size (dh < 2 nm), and have concentrations <0.3 μM. After enrichment with mercury, the complexes formed between the nano-sized components and Hg were analyzed using AF4–ICP-MS. The elution profile of Hg followed the distribution of the UV-absorbing components of DOM, characterized by slightly higher sizes than qB-DOM. Only a small proportion of Hg was associated with the larger-sized components containing Fe and Mn, probably inorganic oxides that were identified in most of the samples from river to lake. The size distribution of the Hg–DOM complexes was enlarged when the concentration of added Hg increased (from 10 to 100 nM). This was explained by the presence of small iron oxides, overlapping the size distribution of Hg–DOM, on which Hg bound to a small proportion. In addition, to provide information on the dispersion of macromolecular thiols in colored DOM-rich natural water, our study also illustrated the potential of AF4–FluoD–UVD–ICP-MS to trace or quantify dynamic changes while Hg binds to the natural nano-colloidal components of surface water.

Loss and Increase of the Electron Exchange Capacity of Natural Organic Matter during Its Reduction and Reoxidation: The Role of Quinone and Nonquinone Moieties

“…The content through fluorescence quantification might correspond only the surface thiol of NOM but not total thiol. In addition, the thiol content may be underestimated by this fluorescence quantification due to inner-filter effect of NOM . Therefore, the actual contribution of sulfur groups to EAC might be higher than the estimation from fluorescence quantification.…”

“…In addition, the thiol content may be underestimated by this fluorescence quantification due to inner-filter effect of NOM. 43 Therefore, the actual contribution of sulfur groups to EAC might be higher than the estimation from fluorescence quantification. For example, the thiol content in SRNOM measured by EXAFS was approximately 17 times that of the fluorescence method; 42 in other words, the contribution of sulfur groups in SRNOM to EAC might be 1.35%.…”

Thioxobimanes

“… 7 These small fluorophores have been highly instrumental in the development of biochemical methodologies, mainly those involving the detection and analysis of sulfhydryl species, such as H 2 S and glutathione, both in vitro and in vivo. 8 They have also made notable contributions to a variety of biologically related disciplines like enzymology, 9 pharmacology, 10 toxicology, 11 and environmental studies 12 and have also been applied, among other things, in fundamental investigations of photophysical processes 13 and even as photolabile protecting groups. 14 …”