Investigation of DGT as a metal speciation technique for municipal wastes and aqueous mine effluents

This paper reports the results of an investigation on the performance of the Diffusive Gradient in Thin Films (DGT) Technique in speciation of metals in aqueous samples of municipal wastes and mine effluents. The DGT was assessed regarding its suitability for in situ determination of metal speciation in municipal wastes and aqueous mine effluents. As the thickness of the diffusive gel layer of the DGT was increased to 0.40, 0.80, and 1.60 mm, a decrease in the amount of accumulated metal mass was observed for most of the metals studied in all the effluent samples. However, the results were different from one field-study site to another. Effect of kinetics also was observed in the amount of accumulated metal mass by the DGT. The computer speciation code, Windermere Humic Aqueous Model (WHAM VI), was used to predict the metal speciation of Cd, Cu, Ni, Pb, Co, and Zn, and WHAM predictions were compared with those of the experimentally determined metal speciation by the DGT technique (free and labile metal ions). This comparison showed good similarities between the theoretically predicted WHAM VI values and the experimentally measured values by DGT. The DGT technique was found to be simple and useful for investigating chemical speciation of trace metals in aqueous samples of municipal wastes and aqueous mine effluents.     

Use of the diffusive gradients in thin films technique to evaluate (bio)available trace metal concentrations in river water

Concentrations of Cd, Cu, Cr, Pb, Ni and Zn were monitored in the Svitava River (the Czech Republic) during April and September 2005. Total concentrations and total dissolved concentrations were obtained through regular water sampling, and the diffusive gradients in thin films technique (DGT) were used to gain information on the kinetically labile metal concentrations. Each measured concentration was compared with the corresponding average (bio)available concentration calculated from the mass of metal accumulated by the moss species Fontinalis antipyretica. The concentrations of Cd, Pb, Cr and Zn measured using DGT corresponded well with those obtained after the deployment of Fontinalis antipyretica moss bags in the Svitava River, but the concentrations of Cu and Ni did not. The calculated (bio)available Cu concentration correlated well with the total dissolved concentration of Cu, whereas no correlation was found to exist between the concentrations of Ni. Scheme of the Svitava River monitoring station, including the DGT sampling units and Fontinalis antipyretica moss bags Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Assessing oral bioaccessibility of trace elements in soils under worst-case scenarios by automated in-line dynamic extraction as a front end to inductively coupled plasma atomic emission spectrometry

A novel biomimetic extraction procedure that allows for the in-line handing of ≥400 mg solid substrates is herein proposed for automatic ascertainment of trace element (TE) bioaccessibility in soils under worst-case conditions as per recommendations of ISO norms. A unified bioaccessibility/BARGE method (UBM)-like physiological-based extraction test is evaluated for the first time in a dynamic format for accurate assessment of in-vitro bioaccessibility of Cr, Cu, Ni, Pb and Zn in forest and residential-garden soils by on-line coupling of a hybrid flow set-up to inductively coupled plasma atomic emission spectrometry. Three biologically relevant operational extraction modes mimicking: (i) gastric juice extraction alone; (ii) saliva and gastric juice composite in unidirectional flow extraction format and (iii) saliva and gastric juice composite in a recirculation mode were thoroughly investigated. The extraction profiles of the three configurations using digestive fluids were proven to fit a first order reaction kinetic model for estimating the maximum TE bioaccessibility, that is, the actual worst-case scenario in human risk assessment protocols. A full factorial design, in which the sample amount (400–800 mg), the extractant flow rate (0.5–1.5 mL min⁻¹) and the extraction temperature (27–37 °C) were selected as variables for the multivariate optimization studies in order to obtain the maximum TE extractability. Two soils of varied physicochemical properties were analysed and no significant differences were found at the 0.05 significance level between the summation of leached concentrations of TE in gastric juice plus the residual fraction and the total concentration of the overall assayed metals determined by microwave digestion. These results showed the reliability and lack of bias (trueness) of the automatic biomimetic extraction approach using digestive juices.     

Use of the diffusion gradient thin film method to measure trace metals in fresh waters at low ionic strength

The diffusion gradients in thin films (DGT) method was investigated and used to measure trace metal concentrations in river water. The principle of DGT is that trace metal ions diffuse through a thin polyacrylamide gel film (the diffusion gel layer) and are subsequently immobilised and concentrated on a layer of Chelex-100 resin embedded in another polyacrylamide gel film (the resin gel layer). These layers are mounted in a plastic holder, which exposes a fixed area of the diffusion gel layer to the water being monitored. Replacement of the normal agarose cross-linked diffusion gel with bisacrylamide cross-linked gel altered the ion uptake properties of DGT. The bisacrylamide cross-linked gel weakly, and with little selectivity, bound metal ions prior to their irreversible binding to Chelex-100. Trace metal ion uptake by these DGT devices was thus dependent on ionic strength and temperature, although the ionic strength effect is relatively small for most natural waters and negligible in sea water. The concentrations of Cd, Co, Cu, Ni, Pb, and Zn in the Water of Leith, an urban stream in Dunedin, New Zealand, were measured by DGT and the results compared with total dissolved concentrations of these metals measured in conventional (bottle) samples collected in parallel with the DGT monitoring. Greater than 90% of the total dissolved Cd and Zn; 20-40% of the total dissolved Co, Ni, and Pb; and 5% of the total dissolved Cu was available to the DGT method.     

Chemical speciation and contamination assessment of Zn and Cd by sequential extraction in surface sediment of Klang River, Malaysia

The concentration and chemical speciation of Cd and Zn as well as total organic carbon (TOC) were studied in surface sediments from 21 stations along Klang River. Sequential extraction technique (SET) was applied to assess the four (exchangeable, acid-reducible, oxidisable-organic and residual) fractions in surface sediment. And also, to obtain an overall classification of cadmium and zinc pollution in this area. This investigation was the first study on the basis of the chemical speciation of Cd and Zn in surface sediments of the Klang River. The total concentrations of metals were ranged (0.60–2.26 µg g^{− 1}) for Cd and (33.26–268.24 µg g^{− 1}) for Zn. The chemical speciation of Cd and Zn in most sampling stations were in the order of residual > acid-reducible > oxidisable-organic > exchangeable, and it showed that the Zn in Klang River surface sediments existed in the nonresistant fractions, whilst Cd existed in the resistant fraction. The degree of surface sediments contamination was determined for individual contamination factors (ICF) and global contamination factor (GCF). The result of ICF and GCF values showed that those stations located vicinity of municipal area had high potential risk to fauna and flora of the Klang River. The relationship between the concentration of cadmium and zinc at the oxidation-organic fraction with TOC in surface sediment was identified. The results showed that TOC had a positive function to complex with Cd and Zn in the surface sediment of Klang River.     

Simultaneous determination of speciation parameters of Cu,Pb, Cd and Zn in model solutions of Suwannee River fulvic acid by pseudopolarography

There is a growing awareness of the importance of quantitative determinations of speciation parameters of the trace metals Cu, Zn, Cd and Pb in aqueous samples containing chemically heterogeneous humic substances, especially when they are present together, interacting with one another and competing for specific binding sites of the humic substances. Such determinations require fundamental knowledge and understanding of these complex interactions, gained through basic laboratory-based studies of well-characterized humic substances in model solutions. Since the chemical heterogeneity of humic substances plays an important role in the thermodynamics (stability) and kinetics (lability) of trace metal competition for humic substances, a metal speciation technique such as pseudopolarography that can reveal the special, distinctive nature of metal complexation is required, and it was therefore used in this study. A comparison of the heterogeneity parameters (Gamma) for Zn(II), Cd(II), Pb(II) and Cu(II) complexes in model solutions of Suwannee River fulvic acid (SRFA) shows that GammaCd>GammaZn>GammaPb>GammaCu, suggesting that SRFA behaves as a relatively homogeneous complexant for Zn(II) and Cd(II), whereas it behaves as a relatively heterogeneous complexant for Pb(II) and an even more heterogeneous complexant for Cu(II) under the experimental conditions used. The order of values of log K* (from the differential equilibrium function, DEF) for the trace metals at pH 5.0 follow the sequence: log K*Cu>log K*Pb>log K*Zn>log K*Cd. These results are in good agreement with the literature values. The results of this work suggest the possibility of simultaneously determining several metals in a sample in a single experiment, and hence in a shorter time than required for multiple experiments.     

Performance characteristics of suspended particulate reagent-iminodiacetate as a binding agent for diffusive gradients in thin films

The performance characteristics of an alternative binding agent, suspended particulate reagent-iminodiacetate (SPR-IDA), for use with DGT methodology were investigated. The parameters investigated during this study included gel hydration, blank levels, elution factor (f_e), capacity, the effects of pH on the binding of trace metals by DGT. The novel application of this resin for use as a quantitative standard for laser ablation ICP-MS was also evaluated. To further constrain the results for the SPR-IDA binding agent, parallel experiments were performed using resin gel containing Chelex 100, which has been widely reported in the literature. Hydration results showed that the SPR-IDA resin gel reached a stable dimension and weight within ∼30 min and was dimensionally stable for ≤6 months. The measured DGT blanks for the SPR-IDA resin were 0.0023, 0.15, 0.21, 0.0033 and 0.011 ng disc⁻¹ for Co, Ni, Cu, Cd and Pb, respectively. The elution factor differed for the two resin types with the Chelex 100 recoveries slightly lower than previous reports and the SPR-IDA resin showing on average ∼5-9% better recoveries than DGT containing Chelex 100. The measured capacity of DGT discs containing the SPR-IDA binding agent was 0.26 mg Cd, similar to the calculated value of 0.29 mg Cd, indicating the entire resin layer was available for metal uptake.Both resin types performed equally well when deployed in 1 mM NaNO₃ solutions with DGT measurements of ∼100% of direct solution measurements for Co, Ni and Cd. However, DGT measurements of Cu and Pb systematically decreased with increasing solution pH down to ∼50% of solution values at pH 8.0, due to artifacts resulting from colloid formation during the addition of the metals. This was remedied by adding the metals as dilute salt standards and addition of Mg(NO₃)₂ to eliminate adsorption to the container walls. In the latter experiments, DGT measured concentrations of Co, Ni, Cu, Cd and Pb were in agreement with solution concentrations. Deployment of DGT in solutions with increasing concentrations of trace metals yielded linear results, suggesting that quantitative analysis using simplified laser ablation techniques should be possible using this newly characterized SPR-IDA resin gel.     

Measuring bioavailable trace metals from freshwater sediments by diffusive gradients in thin films (DGT) in monitoring procedures for quality assessment

An experimental design using passive samplers was set up in our laboratories with the aim of preparing a procedure for the assessment of trace metals bioavailability in freshwater sediments. Trace metal (Cd, Cu, Pb, Ni, and Zn) bioavailability in sediment samples were measured by diffusive gradients in thin films (DGT) devices and compared to those simultaneously extracted (SEM) in 1N HCl with acid-volatile sulfide (AVS). During experiments DGT devices were exposed at various times (from 4 to 336 h) in sediments with different physical and chemical properties and metal content, after equilibration with ambient water (1:2) for 24 h. Trace metal were progressively accumulated in DGT units and after at least 24-48 h metal fluxes became constant. No relation was found between metal available fractions measured by DGTs and total concentrations in sediments or pore waters. On the contrary good relations were found between available metals measured by DGT and metals simultaneously extracted (SEM) in HCl 1N with acid volatile sulfide (AVS).     

Assessment of a geochemical extraction procedure to determine the solid phase fractionation and bioaccessibility of potentially harmful elements in soils: A case study using the NIST 2710 reference soil

Three mineral acid sequential extraction regimes (HNO₃ only, HNO₃ followed by HCl and aqua regia) were applied to the NIST 2710 contaminated reference soil. The major and trace element chemical analysis data from the extractions were subjected to a chemometric self-modelling mixture resolution procedure which identified that 12 distinct physico-chemical components were extracted. The fractionation of As, Cd, Ni and Pb between these components were determined. Tentative assignments of the mineralogical sources of the components were made. The human ingestion bioaccessible fraction of As, Cd and Pb were determined using the in vitro BARGE UBM bioaccessibility test and were found to be 51.6%, 68.0% and 68.4% respectively. The relationship between the lability of the physico-chemical components and the bioaccessible fraction of the soils was investigated and the bioaccessible fractions were assigned to specific components. The extraction scheme using aqua regia was found to be the most suitable as it was the only one which extracted the iron sulphide phase in the soil.     

Determination of heavy metal traces in metallic materials with IDMS

Summary Two pure copper samples were analysed for Cr, Ni, Zn, Cd, and Pb with isotope dilution mass spectrometry (IDMS) as a part of a certification campaign of the European Community Bureau of Reference in Brussels. Additionally, one commercially available copper powder was determined for Zn, Cd, and Pb. After dissolution of the sample in aqua regia Pb was separated from the matrix by anodic electrodeposition, the other elements by anion-exchange chromatography. Positive thermal ions were produced in a single-filament ion source using the silica gel technique with phosphoric acid for Zn, Cd, and Pb and with boric acid for Cr and Ni. Most of the heavy metals could be determined with relative standard deviations of about 1% down to the ng/g level. The detection limits were 13 ng/g for Zn, 4 ng/g for Ni, 2 ng/g for Cr, 1 ng/g for Pb, and 0.03 ng/g for Cd. The results were compared with those obtained by another IDMS laboratory and by other methods applied during the certification campaign.

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Bestimmung von Schwermetallspuren in metallischen Werkstoffen mit der massenspektrometrischen IsotopenverdünnungsanalyseTeil 1. Bestimmung von Cr, Ni, Zn, Cd und Pb in reinem Kupfer

     

Assessment of trace metal binding kinetics in the resin phase of diffusive gradients in thin films

The dynamic technique of diffusive gradients in thin films (DGT), that measures metal speciation in situ, has found wide environmental application. Simple interpretation of the metal accumulation in terms of a solution concentration has assumed that trace metals do not penetrate beyond the surface of the binding layer, but penetration, although theoretically discussed has not yet been directly measured. Multiple binding layers were used to enable analysis of different depths of a DGT binding phase (Chelex-100 or iminodiacetate resins). In simple metal solution (no ligand) at pH 7, metal penetration to the back layer was low and similar for all metals. However, at lower pH up to 42% of an individual metal accumulated in the back resin layer. This was most noticeable for Mn at pH 4 and 5, but Cd and Co were also affected at pH 4. These results were consistent with rate limited binding, particularly for Mn. A kinetic model successfully fitted the data and allowed derivation of a binding rate constant and the mean distance that metals penetrate into a resin gel (λ_M). Only for Mn, Co and Cd were experimentally derived λ_M values greater than the diameter of a Chelex-100 resin bead. For most situations, then, the penetration into the binding layer is negligible and binding of trace metal ions can be regarded as instantaneous, validating the simple use and interpretation of DGT. For weakly binding metals at low pH the slower binding allows penetration, which may affect the DGT measurement.     

Uranium aqueous speciation in the vicinity of the former uranium mining sites using the diffusive gradients in thin films and ultrafiltration techniques

The performance of the Diffusive Gradients in Thin films (DGT) technique with Chelex^®-100, Metsorb™ and Diphonix^® as binding phases was evaluated in the vicinity of the former uranium mining sites of Chardon and L'Ecarpière (Loire-Atlantique department in western France). This is the first time that the DGT technique with three different binding agents was employed for the aqueous U determination in the context of uranium mining environments. The fractionation and speciation of uranium were investigated using a multi-methodological approach using filtration (0.45 μm, 0.2 μm), ultrafiltration (500 kDa, 100 kDa and 10 kDa) coupled to geochemical speciation modelling (PhreeQC) and the DGT technique. The ultrafiltration data showed that at each sampling point uranium was present mostly in the 10 kDa truly dissolved fraction and the geochemical modelling speciation calculations indicated that U speciation was markedly predominated by CaUO₂(CO₃)₃²⁻. In natural waters, no significant difference was observed in terms of U uptake between Chelex^®-100 and Metsorb™, while similar or inferior U uptake was observed on Diphonix^® resin. In turn, at mining influenced sampling spots, the U accumulation on DGT-Diphonix^® was higher than on DGT-Chelex^®-100 and DGT-Metsorb™, probably because their performance was disturbed by the extreme composition of the mining waters. The use of Diphonix^® resin leads to a significant advance in the application and development of the DGT technique for determination of U in mining influenced environments. This investigation demonstrated that such multi-technique approach provides a better picture of U speciation and enables to assess more accurately the potentially bioavailable U pool.     

Phenolic compounds,antioxidant activity and Cu,Zn, Cd and Pb content in wild and cultivated cranberries and blueberries

The aim of this study was to determine the content of Cu, Zn, Cd and Pb and the total polyphenol (TP) content as well as the total antioxidant capacity (TAC) in wild cranberries and blueberries collected from different localities of the Slovakia and to compare them with properties of six cranberry and six highbush blueberry cultivars obtained from the research centre. Compared with cultivated cranberries (Cu, Zn, Cd and Pb content: 0.642, 1.496, 0.015 and 0.050 mg/kg FM) in wild fruits, higher Cu (by 37%) and lower Zn, Cd and Pb (by 8%, 7% and 44% respectively) were determined using atomic absorption spectrometry method. In wild blueberries, higher Cu, Zn and Pb (by 16%, 209% and 80% respectively) and similar Cd contents were determined compared with cultivated fruits (Cu, Zn, Cd and Pb content: 0.483, 0.541, 0.003 and 0.055 mg/kg FM). The TP contents estimated by spectrophotometry using Folin–Ciocalteau reagent were in intervals 1405–3161 (cranberries) and 1300–3077 (blueberries) expressed as mg GAE/kg FM. While the average TP content determined in wild cranberries was by 31% lower than that in cultivated cranberries, in wild blueberries it was by 97% higher compared with highbush blueberry cultivars. The values of TAC determined by spectrophotometry method using 2,2-diphenyl-1-picrylhydrazyl were in range 20.67–22.22 (cranberries) and 14.03–24.79 (blueberries) expressed as mmol TE/kg FM. In wild cranberries and blueberries, the lower average TAC values compared with cultivated berries were determined (by 1% and 28%, respectively).     

Fractionation and Bioaccessibility of Manganese,Copper, Zinc,Cadmium, and Lead in Commercial Vegetable and Rice Baby Foods Using Inductively Coupled Plasma - Mass Spectrometry (ICP-MS) with Central Composite Design (CCD)

Abstract

Herein the bioaccessibility of Mn, Cu, Zn, Cd, and Pb, selected from essential and toxic elements, was determined in commercially sold vegetable purees intended for infant and toddler consumption. Chemical fractionation studies using water, acetone, diethyl ether, chloroform:methanol, and n-hexane were employed to predict the importance of the protein and lipid parts of a matrix to assess the bioaccessibility data. In addition, in-vitro gastrointestinal digestion was performed to determine the bioaccessibility of the elements using a five level, three factor central composite design (CCD) to maximize the elemental solubility. The total elemental concentrations in all of the fractions were determined by inductively coupled plasma – mass spectrometry (ICP-MS). Based on the consumption of one jar of vegetable/rice-based baby food, Zn was 1.3% of the recommended dietary allowance and Mn was 4.2% of the adequate intake level, while Cu was almost 100% of the adequate intake level. Additionally, Pb was always below the detection limit and Cd was sometimes under the detection limit for the percent bioaccessibility. However, in some samples, Cd was as high as 80% of the tolerable weekly intake level depending on the body weight.     

Metal speciation measurement by diffusive gradients in thin films technique with different binding phases

Since its invention in the mid-1990s, the diffusive gradients in thin films (DGT) technique has rapidly become one of the most promising in situ sampling techniques for trace metal measurement in natural waters. We investigated here the possibility of using DGT devices with different binding phases to determine different DGT labile fractions of Cd and Cu in laboratory solutions and in natural waters. Several binding phases were studied, including conventional Chelex 100 resin imbedded polyacrylamide hydrogel (Chelex) and several recently developed binding phases, poly(acrylamide-co-acrylic acid) (PAM-PAA) gel, poly(acrylamidoglycolic acid-co-acrylamide) (PAAG-PAM) gel, Whatman P81 cellulose phosphate ion-exchange membrane (P81), and poly(4-styrenesulfonate) (PSS) aqueous solution. Laboratory testing in metal solutions spiked with EDTA or humic acid suggested that all the DGT devices measured only free metal ions and inorganic metal complexes. Upon field testing at both freshwater and seawater sites it was found that the DGT labile metal concentrations measured by different binding phases can be significantly different, suggesting that the DGT labile metal fractions were dependent on binding strength of the binding phase. By designing binding phases that can compete with different natural water complexing ligands to varying extents, it is possible to use these different DGT devices to measure metal speciation in natural waters.     

Speciation of copper and zinc in natural freshwater: comparison of voltammetric measurements, diffusive gradients in thin films (DGT) and chemical equilibrium models

In situ measurements of copper and zinc using diffusive gradients in thin films (DGT) in two distinct natural water systems were compared to metal speciation assessed by competitive ligand exchange (CLE) and voltammetric measurements. In a dynamic river system, where dissolved metal concentrations vary significantly over short-time periods, DGT technique provided averaged values of the metal concentrations over time. In microcosms, at different total dissolved concentrations of copper and zinc, DGT technique measured a similar fraction as measurements of labile metal performed by voltammetry. The proportion of DGT and voltammetric-labile zinc to dissolved zinc was 61±4% and, respectively, 76±9%. DGT technique was measuring 81±8% of exchangeable copper (by exchange with catechol). These two fractions were similarly influenced by the addition of NTA. In the absence of NTA, copper measured by DGT represented 34±4% of dissolved copper whereas in the presence of NTA, this proportion raised to 57±2%. These measurements were compared to calculations performed with speciation programs using several models for the complexation by humic and fulvic substances, namely Model VI (WHAM), NICA-Donnan and SHM. The predicted speciation by these three models was similar. The prediction of free zinc ion and labile zinc concentrations were in agreement with experimental data. Calculated concentrations of free copper ion were overestimated because these models are not considering strong specific copper-binding ligands probably present in natural water.     

Study of the Contents and Speciation of Heavy Metals in River sediments By Factor Analysis

Abstract

Heavy metals Zn, Cd, Pb, Cu, Ni and Co from two spanish river sediments have been determined by voltammetric techniques, along with % CaCO₃ and % organic matter, and the whole data set examined by means of Factor Analysis, finding a different behaviour of the metals in each river.

Heavy metal speciation in the sediments was carried out by using the Tessier's scheme: Zn and Pb were mainly associated to ‘reducible phases’, Cd and Cu bound to ‘organic matter and sulphides’, and Ni and Co were distributed between the above fractions. The ‘residual’ metals were used as pollution indicators from the rivers, finding a similar behaviour to other industrialized river systems.     

Solid phase extraction and diffusive gradients in thin films techniques for determination of total and labile concentrations of Cd(II), Cu(II), Ni(II) and Pb(II) in Black Sea water

Total dissolved and labile concentrations of Cd(II), Cu(II), Ni(II) and Pb(II) were determined at six locations of the Bourgas Gulf of the Bulgarian Black Sea coast. Solid phase extraction procedure based on monodisperse, submicrometer silica spheres modified with 3-aminopropyltrimethoxysilane followed by the electrothermal atomic absorption spectrometry (ETAAS) was developed and applied to quantify the total dissolved metal concentrations in sea water. Quantitative sorption of Cd, Cu, Ni and Pb was achieved in the pH range 7.5–8, for 30?min, adsorbed elements were easily eluted with 2?mL 2?mol?L^?1 HNO₃. Since the optimal pH for quantitative sorption coincides with typical pH of Black Sea water (7.9–8.2), on-site pre-concentration of the analytes without any additional treatment was possible. Detection limits achieved for total dissolved metal quantification were: Cd 0.002?µg?L^?1, Cu 0.005?µg?L^?1, Ni 0.03?µg?L^?1, Pb 0.02?µg?L^?1 and relative standard deviations varied from 5–13% for all studied elements (for typical Cd, Cu, Ni and Pb concentrations in Black Sea water). Open pore diffusive gradients in thin films (DGT) technique was employed for in-situ sampling and pre-concentration of the sea water and in combination with ETAAS was used to determine the proportion of dynamic (mobile and kinetically labile) species of Cd(II), Cu(II), Ni(II) and Pb(II) in the sea water. Obtained results showed strong complexation for Cu and Pb with sea water dissolved organic matter. The ratios between DGT-labile and total dissolved concentrations found for Cu(II) and Pb(II) were in the range 0.2–0.4. For Cd and Ni, these ratios varied from 0.6 to 0.8, suggesting higher degree of free and kinetically labile species of these metals in sea water.     

An Electrochemical Study of the Interactions Between Trace Metals and Humic Substances in Freshwaters by Anodic Stripping Voltammetry with a Thin Mercury Film Rotating Disk Electrode

An improved theoretical approach to Anodic Stripping Voltammetry with a Thin Mercury Film Rotating Disk Electrode for elucidating the nature of the interactions of Pb(II), Cd(II) and Zn(II) with humic substances in model solutions of Laurentian fulvic acid, and of Pb(II), Cd(II), Zn(II) and Cu(II) in freshwaters, is presented. Conditional stability constants of Pb(II), Cd(II) and Zn(II) complexes decreased with the ionic potential (z²/r) and increased with softness of the metal ion, indicating strong affinity of soft, polarizable donor ligands on humic substances for softer metal ions, resulting in an appreciable covalent character in electrostatic bonding between the metals and humic substances.     

连续萃取法研究海湾养殖区沉积物中重金属形态

以连续萃取法研究海湾养殖区沉积物中重金属(Cd, Cu, Pb, Zn)的形态,将重金属分离为酸溶态、还原态、有机质结合态、硫化物结合态和残渣态.分别采用基体匹配法和内标法消除高盐基体对电感耦合等离子体光谱法(ICP-OES)和质谱法(ICP-MS)分析结果的影响.对海洋沉积物标准物质分析结果表明,样品稀释后测定值与标准值一致.比较了本连续萃取法和BCR法对沉积物样品中重金属形态的提取结果,并考察了萃取剂的选择性.实验表明,本方法可用于有机质污染和富营养化环境沉积物中重金属形态分析,特别是有机质结合态和硫化物结合态的分析.