Free Zn2+ determination in natural freshwaters of the Pyrenees: towards on-site measurements with AGNES

Current Opinion in Electrochemistry

Galceran

Pinheiro

et al. 2017

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...

“…Possible with SPE. [109] Interferences from other metals or organic matter DOC might interfere, possibly affecting the sensitivity at ligand saturation and, thus, affecting final results.…”

Section: Best Lower Detection Limit Reported Formentioning

confidence: 99%

“…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]. Mercury-free options are the bismuth film 223 deposited on the surface of a glassy carbon solid electrode [110] or the Vibrating Gold 224…”

mentioning

confidence: 99%

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

Current Opinion in Electrochemistry

Galceran

Pinheiro

et al. 2017

“…However, AGNES (Absence of Gradients and Nernstian Equilibrium Stripping) [13,14] was specifically designed to measure free metal ion concentrations for amalgamating ions with negative standard redox potentials. AGNES has dealt with Zn, Cd and Pb, in a range of systems including seawater [15], river water [16][17][18], estuarine water [19], soil extracts [16], wine [20], hydroponic media [21] as well as solutions containing dissolved organic matter [22,23], and nanoparticles [24][25][26][27][28][29][30][31][32]. Very recently, AGNES has been applied to indium solutions with either the hanging mercury drop electrode [33] or the thin film rotating disc electrode [34].…”

Section: Introductionmentioning

confidence: 99%

New methodology to measure low free indium (III) concentrations based on the determination of the lability degree of indium complexes. Assessment of In(OH)3 solubility product

Tehrani

Journal of Electroanalytical Chemistry

Dago

et al. 2019

Self Cite

The vast industrial and consumer application of indium (solar cells, displays, etc.) risks its eventual leakage to the environment. Given the relevant role of speciation on the ecotoxicological effects of a certain total amount of indium, it is crucial to develop proper techniques to determine free concentrations of indium. The electroanalytical technique AGNES (Absence of Gradients and Nernstian Equilibrium Stripping) has already proved useful in such a goal. However, the optimization of suitable deposition times in some conditions might be laborious. This work presents a new strategy, based on the technique ADLC (Accumulation under Diffusion Limited Conditions), to determine lability degrees, which apart from their intrinsic physicochemical interest -by comparing reaction kinetics with diffusion rates-, provide useful guidelines for AGNES deposition times. The suggested novel methodology is illustrated with: i) the computation of lability degrees of indium-oxalate complexes (unreported up to date) and ii) measuring free concentration of indium (for the first time as low as pmol L -1 ) in precipitated solutions (i.e. containing precipitated indium hydroxide in the electrochemical cell). The method takes advantage of the fact that the addition of a suitable concentration of oxalate does not change the free indium concentration (which is buffered due to the existing precipitate at a fix pH), but creates a large amount of published in Journal of Electroanalytical Chemistry 847 (2019) 113185 2/38 labile and mobile indium complexes that contribute to the desired accumulation at very large gains (preconcentration factors). Results confirm the validity of the solubility product of indium hydroxide reported in the database NIST 46.7

“…In the Resin Titration Technique [16] and in the Ion-Exchange Technique [22] the analyte is accumulated in an ionic exchange resin. The electroanalytical technique AGNES [19,23] has proved successful in measuring the free concentration of Zn in a range of systems including natural waters [24][25][26][27], dispersions of nanoparticles [28,29] or wine [30].…”

Section: Introductionmentioning

confidence: 99%

Comparison of different speciation techniques to measure Zn availability in hydroponic media

Galceran

Puy

et al. 2018

Analytica Chimica Acta

Self Cite

Four analytical techniques are compared: AGNES (Absence of Gradients and Nernstian Equilibrium Stripping), LASV (Anodic Stripping Voltammetry with Linear stripping), DGT (Diffusive Gradients in Thin films) and PIM (Polymer Inclusion Membranes). These techniques have been designed to provide the free ion concentration or a labile fraction, complementarily contributing to an integrated description of speciation and availability. Their simultaneous application to the determination of free Zn concentrations or labile fluxes in seven solutions of a hydroponic medium reveals characteristics of each technique and correlations between their results. All dynamic results can be interpreted in terms of a general theoretical framework on fluxes. Indeed, in techniques under diffusion-limited conditions in the sample, the flux can be split into the free contribution (linearly proportional to the free fraction), plus the contribution of the complexes (where mobility, lability and abundance of complexation are intertwined). A methodology to compute lability degrees is developed. Measurements with PIM devices confirm that diffusion in the sample solution is not rate limiting, so its flux is proportional to the free metal in the donor solution. A proportionality between the responses of any given two techniques is observed, which suggests that, for the low ligand-to-metal concentration ratios used in the present work, any of these techniques would correlate similarly with uptake, toxic or nutritional measurements.