Comparison of Analytical Techniques for Dynamic Trace Metal Speciation in Natural Freshwaters

Lancaster University, Lancaster, England, United Kingdom
Environmental Science and Technology (Impact Factor: 5.33). 03/2006; 40(6):1934-41. DOI: 10.1021/es051245k
Source: PubMed


Several techniques for speciation analysis of Cu, Zn, Cd, Pb, and Ni are used in freshwater systems and compared with respect to their performance and to the metal species detected. The analytical techniques comprise the following: (i) diffusion gradients in thin-film gels (DGT); (ii) gel integrated microelectrodes combined to voltammetric in situ profiling system (GIME-VIP); (iii) stripping chronopotentiometry (SCP); (iv) flow-through and hollow fiber permeation liquid membranes (FTPLM and HFPLM); (v) Donnan membrane technique (DMT); (vi) competitive ligand-exchange/stripping voltammetry (CLE-SV). All methods could be used both under hardwater and under softwater conditions, although in some cases problems with detection limits were encountered at the low total concentrations. The detected Cu, Cd, and Pb concentrations decreased in the order DGT > or = GIME-VIP > or = FTPLM > or = HFPLM approximately = DMT (>CLE-SV for Cd), detected Zn decreased as DGT > or = GIME-VIP and Ni as DGT > DMT, in agreement with the known dynamic features of these techniques. Techniques involving in situ measurements (GIME-VIP) or in situ exposure (DGT, DMT, and HFPLM) appear to be appropriate in avoiding artifacts which may occur during sampling and sample handling.

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    • "The present review paper focuses on speciation of trace elements in freshwater by voltammetric techniques, including covalently bound substituents, redox species and elemental forms differing in the nature of their complexed substituents according to the IUPAC definition [2] : dynamic methods, with or without voltammetric detection, have been recently reviewed, [12] [13] whereas a review collecting available speciation and fractionation methods for natural waters may be found in Pesavento et al. [14] Moreover, only methods allowing the direct determination of element species have been dealt with in the current paper: protocols requiring extraction, medium exchange, or any kind of pretreatment (like separation by ion exchange or other kind of columns) were considered outside the focus of the paper as one of the benefit of voltammetric techniques is the possibility to act directly as species-specific probes. The current review aims to give information on three relevant topics: (1) an overview of existing voltammetric speciation methods, with emphasis on practical features: a brief description of the procedure, sample size requirement, analysis time, figures of merit (accuracy, precision, limit of detection); (2) current knowledge in the field of trace element speciation in freshwater bodies, organised by element and matrix (data from 1974 to 2014); (3) future perspectives and needs for freshwater speciation studies. "
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    ABSTRACT: Research in voltammetric speciation methods has been mainly driven by the research interests of the oceanographic scientific community and methods were subsequently adapted to freshwater conditions. Nonetheless, different processes, variability of geological, chemical, biological and ecological settings on the one side, and different human land and water uses on the other imply specific needs and a strong shift in concerns for inland waters in terms of investigated analytes. This review paper focuses on speciation of trace elements in freshwater by voltammetric techniques, giving information on and a critical assessment of the state of the art in this field. Methods determining covalently bound substituents, redox species and element forms differing in the nature of their complexed substituents were considered, according to the IUPAC definition of species. Three relevant topics are discussed: an overview of existing voltammetric speciation methods, with emphasis on practical features; current knowledge in the field of trace element speciation in freshwater bodies, organised by element and matrix; and future perspectives and needs for freshwater speciation studies. As a general outcome, a complete picture of trace element speciation in freshwater matrices is far from being achieved.
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    • "DGT is an in situ passive sampler that gives an average dissolved metal concentration over deployment time (2 days at the experimental start and 2 days at the end). In contrast, UF gives dissolved metal concentration at the sampling time, which was on days 0, 2, 7 and 9. Metal species collected in DGT are those that pass through the diffusive gel layer solely by molecular diffusion and include inorganic species and small labile complexes,[28]whereas in UF the dissolved metal fraction is separated from the particulates by filtration through the filter using centrifugation. In the case of dissolved Ag, which is only weakly bound to DOC,[44]some differences between the species passing through the UF and those diffusing through the DGT gel lead to somewhat higher dissolved concentrations by UF. "
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    ABSTRACT: The dissolution of some widely used nanoparticles (NPs), Ag (citrate coated), ZnO, CuO and Cu-carbon coated (Cu/C), has been studied over a period of 9 days in five different natural waters: wastewater treatment plant effluent (WWTP Du¨bendorf) and lakes Greifen, Lucerne, Grue`re and Cristallina. These waters differ in ionic strength, pH and dissolved organic carbon (DOC). The dissolved fraction of metals from NPs was determined using DGT (diffusion gradients in thin films) and ultrafiltration (UF). ZnO-NPs and CuO-NPs dissolved to a large extent in all waters, whereas the dissolved fraction was much smaller in the case of Cu/C and Ag-NPs. All NPs dissolved to a larger extent in water from Lake Cristallina with low pH, low ionic strength and low DOC. Ag-NP dissolution was favoured at low ionic strength and low pH, whereas dissolution of CuO-NPs was mostly dependent on pH. Cu/C-NPs strongly agglomerated and sedimented and yielded low dissolved Cu concentrations. DGT and UF produced similar results, although these two methods differ in the measurement time scale. The results of this study indicate that dissolution is an important process for these NPs under conditions of natural waters or wastewaters.
    No preview · Article · Mar 2015 · Environmental Chemistry
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    • "In a comprehensive study, DGT was deployed in situ in river and lake water alongside another in situ dynamic technique, the gel integrated microelectrode (GIME) variant of voltammetry, and two techniques for measuring free ions, namely Donnan membrane (DMT) (in situ) and permeable liquid membrane (PLM) (laboratory). [14] "
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    ABSTRACT: This review assesses progress in studies of chemical speciation using diffusive gradients in thin-films (DGT) by examining the contributions made by key publications in the last 20 years. The theoretical appreciation of the dynamic solution components measured by DGT has provided an understanding of how DGT measures most metal complexes, but excludes most colloids. These findings strengthen the use of DGT as a monitoring tool and provide a framework for using DGT to obtain in situ kinetic information. Generally, the capabilities of DGT as an in situ perturbation and measurement tool have yet to be fully exploited. Studies that have used DGT to investigate processes relevant to bioavailability have blossomed in the last 10 years, especially for soils, as DGT mimics the diffusion limiting uptake conditions that, under some conditions, characterise uptake by plants. As relationships between element accumulated by DGT and in plants depend on the plant species, soils studied, and the element and its chemical form, DGT is not an infallible predictive tool. Rather its strength comes from providing information on the labile species in the system, whether water, soil or sediment. Recent studies have shown good relationships between measurements of metals in periphyton and by DGT, and unified dose response curves have been obtained for biota in sediments when they are based on DGT measurements. Both these cases suggest that alternative approaches to the established ` free ion' approach may be fruitful in these media and illustrate the growing use of DGT to investigate environmental chemical processes.
    Full-text · Article · Jan 2015 · Environmental Chemistry
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