Dynamic DGT speciation analysis and applicability to natural heterogeneous complexes

2009 ◽  
Vol 6 (2) ◽  
pp. 170 ◽  
Author(s):  
Raewyn M. Town ◽  
Parthasarathi Chakraborty ◽  
Herman P. van Leeuwen
Keyword(s):  
Thin Film ◽  
Thermodynamic Stability ◽  
Metal Ion ◽  
Natural Waters ◽  
Speciation Analysis ◽  
Metal Species ◽  
Kinetic Regime ◽  
Ligand Ratio ◽  
Diffusive Gradients ◽  
Kinetic Features

Environmental context. The environmental fate and bioavailability of metal ions in natural waters is determined by their thermodynamic stability and kinetic features, both of which are distributed and depend on the metal ion loading of the system. Diffusive gradients in thin film (DGT) is a dynamic technique for metal speciation analysis that measures a certain portion of these complexes as determined by its operational timescale. Reliable interpretation of data furnished by DGT necessitates characterisation of its features for the particular case of heterogeneous complexes. Abstract. Owing to their inherent heterogeneity, the thermodynamic stability of metal ion complexes with natural ligands is characterised by a distribution, and thus is a function of metal-to-ligand ratio. The kinetic features of such metal complexes are also distributed and can be probed by dynamic speciation techniques. The kinetic regime of the metal complex sample can be manipulated via the metal-to-ligand ratio, and the timescale over which kinetic parameters are actually in effect is defined by the window of the chosen technique. Here we detail the kinetic features of diffusive gradients in thin film (DGT), and show that the range of attainable measurement timescales (τ) is rather limited: variation of the gel layer thickness practically allows only one order of magnitude in τ to be scanned. The more effective use of DGT to probe the distribution of dynamic metal species in heterogeneous systems is via variation of the metal-to-ligand ratio in the sample solution. Compilation of the literature DGT data for natural waters shows that by assuming a Freundlich isotherm relationship, the degree of heterogeneity is reflected in the measured DGT concentration as a function of metal ion loading.

Contribution of organic arsenic species to total arsenic measurements using ferrihydrite-backed diffusive gradients in thin films (DGT)

2012 ◽  
Vol 9 (1) ◽  
pp. 55 ◽  
Author(s):  
Heléne Österlund ◽  
Mikko Faarinen ◽  
Johan Ingri ◽  
Douglas C. Baxter
Keyword(s):  
Thin Films ◽  
Natural Waters ◽  
Arsenic Speciation ◽  
Inorganic Arsenic ◽  
Speciation Analysis ◽  
Arsenic Species ◽  
Future Studies ◽  
Organic Arsenic ◽  
Arsenic Determination ◽  
Diffusive Gradients

Environmental contextBoth the mobility and toxicity of arsenic in natural waters are related to the aqueous species distribution. Passive sampling using ferrihydrite-backed diffusive gradients in thin films (DGT) devices has in previous studies been characterised to measure labile inorganic arsenic, and the possible contribution of organic species has been disregarded. This study shows that the two most prevalent organic arsenic species might be included in DGT measurements, which should be taken into consideration when evaluating DGT data in future studies. AbstractIn previous publications discussing arsenic determination using ferrihydrite-backed diffusive gradients in thin films (DGT) devices, organic arsenic forms have been disregarded, even though it is known that the two most prevalent in natural waters, dimethylarsinate (DMA) and monomethylarsonate (MMA), may adsorb to ferrihydrite and thereby be included in the measurement. In this work the accumulation of DMA and MMA, as well as inorganic arsenite and arsenate, to ferrihydrite-backed DGT devices was investigated. It could be demonstrated that MMA, and under acidic conditions also DMA, adsorbed to the binding layer and might therefore contribute to the total mass of measured arsenic. Diffusion coefficients were measured for all four species to enable quantification of DGT-labile concentrations of organic and inorganic arsenic. Elution of the analytes from the ferrihydrite binding layer was performed using 1 mL of 1 M NaOH to facilitate arsenic speciation analysis using chromatographic separation. Average recovery rates were between 87 and 108 %. This study shows that the contribution of DMA and MMA to the total accumulated mass must be taken into consideration when evaluating DGT data in future studies.

Dynamic features of speciation analysis by adsorptive stripping techniques

2010 ◽  
Vol 7 (3) ◽  
pp. 242 ◽  
Author(s):  
Raewyn M. Town ◽  
Herman P. van Leeuwen
Keyword(s):  
Ligand Exchange ◽  
Natural Waters ◽  
Environmental Fate ◽  
Metal Speciation ◽  
Speciation Analysis ◽  
Dynamic Features ◽  
Natural Systems ◽  
Surface Active ◽  
The Stability ◽  
Kinetic Features

Environmental context.The environmental fate and bioavailability of metal ions in natural waters is determined by their thermodynamic stability and kinetic features, both of which are distributed. Competing ligand exchange – adsorptive stripping (CLE-AdS) is a technique that measures a certain portion of these complexes as determined by the stability of the selected competing ligand and the dynamic features of the sample complexes that remain following ligand exchange. Exploitation of CLE-AdS to determine a spectrum of sample complexes requires insight into its thermodynamic and kinetic windows. Abstract.The kinetic features of the accumulation step of competing ligand exchange – adsorptive stripping (CLE-AdS) in metal speciation methodology are elaborated. During the adsorptive accumulation process, the flux of the surface active complex MLad towards the electrode may be modified by the coupled conversions of ML and M into MLad. An immediate consequence is that the accumulation flux of MLad can be greater than that corresponding to its mere bulk concentration: a labile ML contributes fully to the MLad accumulation, and a further flux enhancement can arise if ML is more mobile than MLad (DML > DMLad). Applying the conventional lability criterion, we present a framework for interpretation of CLE-AdS measurements in the presence of kinetic contributions from sample ML to the adsorptive accumulation of MLad. Measured accumulation fluxes for a kinetic case are well described by the presented theoretical framework. The dynamic analysis provides the basis for exploitation of CLE-AdS over a wider kinetic window than has been used to date. Consideration of the dynamics of sample species during the adsorptive accumulation step is fundamental for interpretation of metal speciation by CLE-AdS in complex natural systems that contain a distribution of complexes of different stability, lability, and mobility.

Gel–water partitioning of soil humics in diffusive gradient in thin film (DGT) analysis of their metal complexes

2012 ◽  
Vol 9 (1) ◽  
pp. 24 ◽  
Author(s):  
Pascal L. R. van der Veeken ◽  
Herman P. van Leeuwen
Keyword(s):  
Thin Film ◽  
Metal Complexes ◽  
Metal Speciation ◽  
Speciation Analysis ◽  
Fulvic Acids ◽  
Metal Species ◽  
Environmental Media ◽  
Gel Layer ◽  
Basic Features ◽  
Flux Response

Environmental contextMetal species can have significant toxic effects in aquatic systems, and therefore their occurrence should be reliably monitored. Although many methods to measure metal species are available, they all have limitations and are sensitive to physicochemical complications. It is shown that, in techniques based on diffusive gradients in thin films, sorption of humic acids affects metal speciation inside the diffusive gel layer and the nature of the ensuing flux response. AbstractMetal complexes of humic and fulvic acids are ubiquitous in aqueous environmental media. In metal speciation analysis by DGT (diffusive gradient in thin film) with polyacrylamide hydrogels, soil humic acid species have been shown to significantly accumulate in the diffusive gel layer. As a result, the speciation of their metal complexes inside the gel is changed with respect to that in the sample medium. In low ionic strength samples, the effects of sorption of the charged humic species are compounded by Donnan partitioning. Here we lay out the basic features that govern the partition of humic species between gel and water, and discuss their effect on the properties of the DGT metal flux.

Protonation effects on dynamic flux properties of aqueous metal complexes

2009 ◽  
Vol 74 (10) ◽  
pp. 1543-1557 ◽  
Author(s):  
Herman P. Van Leeuwen ◽  
Raewyn M. Town
Keyword(s):  
Complex Formation ◽  
Metal Ion ◽  
Good Description ◽  
Minor Component ◽  
Outer Sphere ◽  
Metal Species ◽  
Central Metal ◽  
Inner Sphere ◽  
A Minor ◽  
Protonated Ligand

The degree of (de)protonation of aqueous metal species has significant consequences for the kinetics of complex formation/dissociation. All protonated forms of both the ligand and the hydrated central metal ion contribute to the rate of complex formation to an extent weighted by the pertaining outer-sphere stabilities. Likewise, the lifetime of the uncomplexed metal is determined by all the various protonated ligand species. Therefore, the interfacial reaction layer thickness, μ, and the ensuing kinetic flux, Jkin, are more involved than in the conventional case. All inner-sphere complexes contribute to the overall rate of dissociation, as weighted by their respective rate constants for dissociation, kd. The presence of inner-sphere deprotonated H2O, or of outer-sphere protonated ligand, generally has a great impact on kd of the inner-sphere complex. Consequently, the overall flux can be dominated by a species that is a minor component of the bulk speciation. The concepts are shown to provide a good description of experimental stripping chronopotentiometric data for several protonated metal–ligand systems.

scholarly journals A New Nanocomposite Packaging Based on LASiS-Generated AgNPs for the Preservation of Apple Juice

Antibiotics ◽  
2021 ◽  
Vol 10 (7) ◽  
pp. 760
Author(s):  
Maria Chiara Sportelli ◽  
Antonio Ancona ◽  
Annalisa Volpe ◽  
Caterina Gaudiuso ◽  
Valentina Lavicita ◽  
...  
Keyword(s):  
Metal Ion ◽  
Chemical Characterization ◽  
Average Diameter ◽  
Biological Action ◽  
Metal Species ◽  
Ion Release ◽  
Bioactive Materials ◽  
Transmission Electron ◽  
Metal Ion Release ◽  
Bulk Chemical

Designing bioactive materials, with controlled metal ion release, exerting a significant biological action and associated to low toxicity for humans, is nowadays one of the most important challenges for our community. The most looked-for nanoantimicrobials are capable of releasing metal species with defined kinetic profiles, either by slowing down or inhibiting bacterial growth and pathogenic microorganism diffusion. In this study, laser ablation synthesis in solution (LASiS) has been used to produce bioactive Ag-based nanocolloids, in isopropyl alcohol, which can be used as water-insoluble nano-reservoirs in composite materials like poly(3-hydroxybutyrate-co-3-hydroxyvalerate). Infrared spectroscopy was used to evaluate the chemical state of pristine polymer and final composite material, thus providing useful information about synthesis processes, as well as storage and processing conditions. Transmission electron microscopy was exploited to study the morphology of nano-colloids, along with UV-Vis for bulk chemical characterization, highlighting the presence of spheroidal particles with average diameter around 12 nm. Electro-thermal atomic absorption spectroscopy was used to investigate metal ion release from Ag-modified products, showing a maximum release around 60 ppb, which ensures an efficient antimicrobial activity, being much lower than what recommended by health institutions. Analytical spectroscopy results were matched with bioactivity tests carried out on target microorganisms of food spoilage.

Fabrication and Photoelectrochemical Characterization of Fe, Co, Ni and Cu-Doped TiO2 Thin Films

2013 ◽  
Vol 764 ◽  
pp. 266-283 ◽  
Author(s):  
Ibram Ganesh ◽  
Rekha Dom ◽  
P.H. Borse ◽  
Ibram Annapoorna ◽  
G. Padmanabham ◽  
...  
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Metal Ions ◽  
Band Gap ◽  
Metal Ion ◽  
Band Gap Energy ◽  
Chemical Compositions ◽  
Gap Energy ◽  
Glass Substrates ◽  
Photoelectrochemical Characterization

Different amounts of Fe, Co, Ni and Cu-doped TiO2 thin films were prepared on fluorine doped tin oxide (FTO) coated soda-lime glass substrates by following a conventional sol-gel dip-coating technique followed by heat treatment at 550 and 600°C for 30 min. These thin films were characterized for photo-current, chronoamperometry and band-gap energy values. The chemical compositions of metals-doped TiO2 thin films on FTO glass substrates were confirmed by XPS spectroscopic study. The metal-ions doped TiO2 thin films had a thickness of <200 nm="" optical="" transparency="" of="">80%, band-gap energy of >3.6 eV, and a direct band-to-band energy transition. The photoelectrochemical (PEC) studies revealed that all the metal-ions doped TiO2 thin films exhibit n-type semi-conducting behavior with a quite stable chronoamperometry and photo-currents that increase with the increase of applied voltage but decrease with the dopant metal-ion concentration in the thin film. Furthermore, these thin films exhibited flat-band potentials amenable to water oxidation reaction in a PEC cell. The 0.5 wt.% Cu-doped TiO2 thin film electrode exhibited an highest incident photon-to-current conversion efficiency (IPCE) of about 21%.

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