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.
    Environmental Chemistry 07/2015; DOI:10.1071/EN14233 · 2.51 Impact Factor
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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.
    Environmental Chemistry 01/2015; 12(2). DOI:10.1071/EN14105 · 2.51 Impact Factor
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    • "Several techniques have been developed for speciation studies of nickel in aqueous solutions; among them competing ligand-exchange methods [6,7,8], ion exchange [9], diffusion gradients in thin films [8,10,11], capillary electrophoresis [12], and membrane-based techniques (ultrafiltration [11], Donnan membrane technique [8,13], and liquid membranes [8,14,15]). The latter techniques offer excellent performance using simple equipment and the reliability of their results for some metal ions and organic pollutants has been favorably compared with bioavailability tests using model microorganisms [16,17]. "
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    ABSTRACT: Nickel (II) preconcentration and speciation analysis using a hollow fiber supported liquid membrane (HFSLM) device was studied. A counterflow of protons coupled to complexation with formate provided the driving force of the process, while Kelex 100 was employed as carrier. The influence of variables related to module configuration (acceptor pH and carrier concentration) and to the sample properties (donor pH) on the preconcentration factor, E, was simultaneously studied and optimized using a 3 factor Doehlert matrix response surface methodology. The effect of metal concentration was studied as well. Preconcentration factors as high as 4240 were observed depending on the values of the different variables. The effects of the presence of inorganic anions (NO2-, SO42-, Cl-, NO3-, CO32-, CN-) and dissolved organic matter (DOM) in the form of humic acids were additionally considered in order to carry out a speciation analysis study. Nickel preconcentration was observed to be independent of both effects, except when cyanide was present in the donor phase. A characterization of the transport regime was performed through the analysis of the dependence of E on the temperature. E increases with the increase in temperature according to the equation E(K) = -8617.3 + 30.5T with an activation energy of 56.7 kJ mol-1 suggesting a kinetic-controlled regime. Sample depletion ranged from 12 to 1.2% depending on the volume of the donor phase (100 to 1000 mL, respectively).
    12/2011; 1(3):217-231. DOI:10.3390/membranes1030217
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