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.

Dynamic Speciation Analysis of Heterogeneous Metal Complexes with Natural Ligands by Stripping Chronopotentiometry at Scanned Deposition Potential (SSCP)

2004 ◽  
Vol 57 (10) ◽  
pp. 983 ◽  
Author(s):  
Raewyn M. Town ◽  
Herman P. van Leeuwen
Keyword(s):  
Metal Complexes ◽  
Humic Substances ◽  
Metal Binding ◽  
Metal Speciation ◽  
Speciation Analysis ◽  
Deposition Potential ◽  
Stripping Chronopotentiometry ◽  
Determination Of Parameters ◽  
Apparent Stability

Stripping chronopotentiometry at scanned deposition potential (SSCP) allows chemical heterogeneity in metal speciation to be unambiguously identified. In the labile regime, use of the Freundlich binding isotherm allows straightforward determination of parameters to describe the apparent stability and heterogeneity of metal complexes with humic substances. The extent of heterogeneity of metal binding by several humic substances follows the order Cu(ii) >> Pb(ii) > Cd(ii). The lability of metal complexes decreases from the foot to the top of the wave, and the greater the degree of heterogeneity, the more readily lability is lost. In the kinetic current regime, the Koutecký–Koryta approximation allows an expression to be obtained for the SSCP wave that provides a good estimate of the experimental data for metal complexes with moderate degrees of heterogeneity.

Steady-state DGT fluxes of nanoparticulate metal complexes

2011 ◽  
Vol 8 (5) ◽  
pp. 525 ◽  
Author(s):  
Herman P. van Leeuwen
Keyword(s):  
Metal Complexes ◽  
Metal Ion ◽  
Chemical Species ◽  
Time Resolved ◽  
Complex Species ◽  
Environmental Media ◽  
Gel Layer ◽  
Simple Limit ◽  
Free Metal ◽  
Free Metal Ion

Environmental contextDiffusive gel layer techniques can measure fluxes of chemical species in aqueous environmental media. Nanoparticulate metal complexes are small enough to penetrate gels, but their diffusive response is much slower than that of the free metal ions. Hence, time-resolved analysis of the diffusive flux of the complex sample is proposed as a chemical speciation tool for the nanodomain. AbstractFor a fully labile complex system, the diffusive gradients in thin film (DGT) metal flux approaches the fairly simple limit defined by the joint diffusion of the free metal ion and the complex species in the gel layer. Natural soft nanoparticulate complexes, such as those with humics and fulvics, generally enter the DGT gel phase and some of them may even be adsorbed by the gel matrix. The time characteristics of the DGT response are affected by a lower rate of diffusion, as well as by possible accumulation of nanoparticulate species in the gel layer. Several cases are discussed in some detail on the basis of numerical analysis of the diffusion process. If the difference between the diffusion coefficients of the free metal ion and the nanoparticulate complex is sufficiently large, the time-resolved DGT flux allows for distinction between these two types of species.

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.

Metal and phosphate speciation during anaerobic digestion of phosphorus rich sludge

1997 ◽  
Vol 36 (6-7) ◽  
pp. 191-200 ◽  
Author(s):  
C. M. Carliell ◽  
A. D. Wheatley
Keyword(s):  
Anaerobic Digestion ◽  
Metal Speciation ◽  
Extraction Methods ◽  
Phosphate Removal ◽  
Metal Species ◽  
Chemical Extraction ◽  
Inorganic P ◽  
Similar Work ◽  
Extractable P ◽  
Phosphate Speciation

Chemical extraction methods are used to investigate metal and phosphate speciation during anaerobic digestion of phosphorus-rich sludge. Tests were performed using model compounds to evaluate the efficacy of the reagents in the extraction sequences and these results compared with similar work by other researchers. The metal speciation method was found to be suitable for identifying shifts in metal distribution but was unrepresentative of actual metal species. The phosphate speciation method did give adequate separation of the phosphate compounds tested. Full-scale digesters treating chemical and biological phosphate removal (CPR and BPR) sludge were analysed according to the methods developed. Results show that digestion of CPR sludge did not increase the soluble P concentration in the digester and that most of the precipitated phosphorus appeared to be retained in the sludge as inorganic P. The digester treating BPR sludge showed increased soluble and water-extractable P, in comparison to the control digester. Trace metal speciation profiles were found to be affected by addition of CPR sludge.

Metal Speciation in Separate Stormwater Systems

1990 ◽  
Vol 22 (10-11) ◽  
pp. 53-60 ◽  
Author(s):  
G. M. P. Morrison ◽  
D. M. Revitt ◽  
J. B. Ellis
Keyword(s):  
Organic Material ◽  
Metal Speciation ◽  
Anodic Stripping Voltammetry ◽  
Toxic Metal ◽  
Stripping Voltammetry ◽  
High Volume ◽  
Suspended Solid ◽  
Metal Species ◽  
The Road ◽  
Organic Complexes

Biogeochemical processes, affecting metal speciation in a gullypot system and at stormwater outfalls, are investigated. Ionic Pb and Cu species released from road sediments by add rain are scavenged by dissolved organic material and suspended solids as a result of a rise in pH through the road/gullypot system. Cadmium and Zn tend to remain in the dissolved phase. Bacterial activity and add dissolution produce increases in dissolved metal in the gullypot liquor and it is these metals which contribute to the early storm profile. Metals in basal gullypot sediments are readily mobilised during high volume/intensity storms. The resulting stormwater contains dissolved ionic forms of Cd and Zn, while Pb is mostly adsorbed to suspended solid surfaces. Copper also binds to solids, although approximately 50% is transported by dissolved organic material (molecular weight ≈ 1000-5000). For the separation of directly toxic metal species, anodic stripping voltammetry at polymer coated electrodes is preferred. Lead and Cu are present as iron/humic colloids and organic complexes respectively, which are not directly toxic to algae. Cadmium is predominantly ionic and inorganically complexed and therefore directly toxic. It is recommended that the highly toxic lipid soluble metal species should be analysed in stormwater.

scholarly journals Interactions of hydrophobic metal complexes and their constituents with aquatic humic substances

2007 ◽  
Vol 4 (5) ◽  
pp. 323 ◽  
Author(s):  
Amiel Boullemant ◽  
Jean-Pierre Gagné ◽  
Claude Fortin ◽  
Peter G. C. Campbell
Keyword(s):  
Metal Complexes ◽  
Humic Substances ◽  
Natural Waters ◽  
Hydrophobic Interactions ◽  
Equilibrium Dialysis ◽  
Fulvic Acids ◽  
Suwannee River ◽  
Dissolved Humic Substances ◽  
Ph Range

Environmental context. Lipophilic metal complexes, because they can readily cross biological membranes, are especially bioavailable. However, in natural waters these complexes do not necessarily exist in a free state, i.e. they may bind to the organic matter (humic substances) that is present in natural waters. It follows that the in situ bioavailability of lipophilic metal complexes will tend to be less than that measured in simple laboratory experiments. Abstract. The ability of dissolved humic substances (HS: fulvic and humic acids) to complex cationic metals is well known, but their interactions with neutral lipophilic metal complexes are little understood. In the present study, we have examined the behaviour of two such complexes ( Cd  L 2 0 -->Cd L02: L = DDC = diethyldithiocarbamate, or L = XANT = ethylxanthate) in the presence of Suwannee River Humic and Fulvic acids. Interactions between the neutral complexes and the humic substances were assessed by excitation-emission matrix (EEM) fluorescence spectroscopy at pH 5.5 and 7.0, and by equilibrium dialysis experiments (500 Da cut-off). The EEM measurements were carried out by titrating the humic substances (6.5 mg C L–1) with Cd, in the absence or presence of ligand L (1 µM DDC or 100 µM XANT). Given the very high stability constants for the complexation of cadmium by DDC and XANT and the excess ligand concentration, virtually all (>96%) of the Cd added to the L + HS matrix was calculated to be present as the neutral Cd L 2 0 -->CdL20 complex over the entire pH range tested. For both humic substances, addition of DDC or XANT alone led to shifts in the fluorescence spectra at both pH values, indicating that the DDC– and XANT– anions likely interact by electrostatic or hydrogen bonding within the humic molecules. The subsequent addition of Cd to these L + HS systems resulted in a disproportionately large enhancement of the fluorescence intensities of individual EEM peaks, this fluorescence enhancement being only slightly decreased by the shift from pH 7.0 to 5.5. We interpret this enhancement as evidence that the two neutral complexes associate with the humic substances, presumably by forming ternary complexes (Ln-Cd-HS). Hydrophobic interactions between the humic substances and the neutral complexes may also contribute, but to a lesser extent, as demonstrated by partitioning calculations based on the lipophilicity of the neutral complexes. The association of the neutral complexes with Suwannee River Humic Acid was confirmed by dialysis experiments.

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