The use of microelectrodes with AGNES

Huidobro, C.; Companys, Encarnació; Puy, Jaume; Galceran, Josep; Pinheiro, José Paulo

doi:10.1016/j.jelechem.2007.06.001

Cited by 22 publications

(19 citation statements)

References 14 publications

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“…Principles of AGNES AGNES has been presented with great detail in previous works. [22][23][24][25][26] We summarise here the principles of this electroanalytical technique which consists of two stages: deposition (first stage) and stripping (second stage).…”

Section: Theoretical Backgroundmentioning

confidence: 99%

Humic acid complexation to Zn and Cd determined with the new electroanalytical technique AGNES

2007

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Environmental context. Humic substances are complex mixtures that play an important role in trace metal bioavailability in soils and aquatic environments. The bioavailability of a metal depends on what chemical forms, or species, it is in. We need to know how much of the metal is present as a free metal ion in solution, and how much is bound up in complexes with humic acids, for example. This work reports the complexation of Cd and Zn to humic acids by means of a simple and robust technique, AGNES (absence of gradients and Nernstian equilibrium stripping). Abstract. AGNES (absence of gradients and Nernstian equilibrium stripping), an emerging electroanalytical technique specifically designed for the determination of the free concentration of heavy metals in aqueous solutions, is here implemented to characterise the binding of CdII and ZnII to a soil humic acid. A set of metal titration experiments were performed by adding Cd or Zn to a purified humic acid (Aldrich) at pH 4, 5, 6 and 7 and measuring the free metal concentration by AGNES. The application of a program with two potential steps along the deposition stage allows for the reduction of the deposition time in the humic titration. The polyelectrolytic effects of the macromolecular ligand were taken into account through the Donnan model. Data free of electrostatic effects were reasonably described by the NICA isotherm, which accounts for heterogeneity, considering just a monomodal distribution (because of the range of pH covered). The obtained affinity parameters indicate a similar strength for Zn and Cd binding to the purified humic acid.

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Section: Theoretical Backgroundmentioning

confidence: 99%

Humic acid complexation to Zn and Cd determined with the new electroanalytical technique AGNES

2007

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“…Its application to a variety of systems, ranging from synthetic solutions to Mediterranean seawater, has been extensively validated on theoretical grounds or with consolidated techniques such as Ion Selective Electrode, Resin Titration or Scanned Stripping Chronopotentiometry [2][3][4][5][6][7][8][9]. The key idea of AGNES is the preconcentration of reduced metal (Zn°in this work) inside the amalgam up to the equilibrium value (set by the applied potential and Nernst equation).…”

Section: Introductionmentioning

confidence: 99%

The impact of high Zn° concentrations on the application of AGNES to determine free Zn(II) concentration

Galceran

Chito

Martínez-Micaelo

et al. 2010

Journal of Electroanalytical Chemistry

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a b s t r a c t AGNES (Absence of Gradients and Nernstian Equilibrium Stripping) determination of free Zn(II) in a solution can be affected by the reaching of high Zn°concentrations inside the amalgam. At concentrations about the solubility limit of Zn°in mercury, the formation of dendrites and powders around the mercury surface can be seen with an optical microscope. At concentrations of Zn°quite below the solubility limit, an anomalous stripping current appears which increases with decreasing supporting electrolyte concentration. The current along the stripping time exhibits a convex shape, which is labelled here as ''anomalous convex behaviour" (acb). The origin of acb is tentatively ascribed to different kinetic reasons (amongst which the electroneutrality limitation due to low ionic strength outstands), but more than one cause is necessary for a full account of the experimental observations. With various strategies, like monitoring the charge as response function or by application of lower gains, AGNES can successfully probe these high concentrations.

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“…Other mercury-based electrodes used are the Hg-Ir microelectrode [106], the rotating 221 disk electrode [107] and the screen printed electrode, SPE [108]. The SPE is specially 222 indicated for in situ applications [109].…”

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A review on electrochemical methods for trace metal speciation in environmental media

Companys

Galceran

Pinheiro

et al. 2017

Current Opinion in Electrochemistry

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11Trace metal speciation is key to understand/predict bioavailability and potential toxicity 12 of metals to biota and will, undoubtedly, be incorporated in future regulations. 13Electroanalytical methods have a role to play in such development: they offer a wide 14 range of advantages such as speed, portability, economy, solid interpretation 15 backgrounds and low limits of quantification. This review focusses on three selected 16 stripping techniques: Competitive-Ligand Exchange -Cathodic Stripping Voltammetry 17 (CLE-CSV), Scanned Stripping Chrono-Potentiometry (SSCP) and AGNES (Absence 18 of Gradients and Nernstian Equilibrium Stripping) reporting their working principles, 19 characteristics (strong and weak points) and recent applications to systems of 20 environmental relevance (such as seawaters, freshwaters or soil extracts). 21 22 23 24 Keywords: speciation, availability, electroanalysis, electrochemistry, heavy metal, 25 CLE-CSV, SSCP, AGNES 26 27 published in Current Opinion 3 (2017) 144-162 33 Speciation (i.e. the distribution of an element among its different chemical forms[1]) 34 has been recognised as a key factor for trace metal (bio)availability to biota, as 35 postulated by hegemonic ecotoxicological paradigms such as the Free Ion Activity 36 Model (FIAM) [2] or the Biotic Ligand Model (BLM)[3], both assuming that the free 37 ion is the only bioavailable species. The limits of these models have recently been 38 reviewed [4], highlighting numerous cases where specific fractions of metal complexes 39 can be internalized, either directly or through the dissociation of labile complexes. Thus, 40there is a need to design, develop, apply and interpret analytical techniques able to 41 provide reliable speciation information [5][6][7] that can be used by regulatory bodies. 42Although there are numerous non-electrochemical techniques [5][6][7][8][9][10][11][12][13], those that are 43 provide attractive possibilities such as speed of analysis, low-cost and miniaturization in 44 view to on-site (and in-situ) measurements [14], and can also provide thermodynamic 45 (i.e. equilibrium) information (such as the amount of the free metal, the amount of 46 complexing sites, the stoichiometry of complexes and their stability constants [15]) as 47 [16;17]. Stripping techniques, due to their low detection limits, are well suited for 50 environmental analysis. They are two-stage techniques, where the first stage is a 51 deposition step that accumulates the analyte (at the electrode surface or in its volume), 52 followed by a second stage that quantifies this analyte. Anodic Stripping Voltammetry 53 (ASV), in its multiple variants, is the most popular and has the advantage to possibly be 54 measuring a potentially bioavailable fraction of the metal, as shown again recently 55 [18;19]. 56 57 published in Current Opinion 3 (2017) 144-162 This critical evaluation focusses on three techniques that are known powerful tools for 58 metal speciation: AGNES (Absence of Gradients and Nernstian Equilibrium Stripping) 59 and SSCP...

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The use of microelectrodes with AGNES

Cited by 22 publications

References 14 publications

Humic acid complexation to Zn and Cd determined with the new electroanalytical technique AGNES

Humic acid complexation to Zn and Cd determined with the new electroanalytical technique AGNES

The impact of high Zn° concentrations on the application of AGNES to determine free Zn(II) concentration

A review on electrochemical methods for trace metal speciation in environmental media

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