Trace metal speciation and bioavailability in surface waters of the Black Sea coastal area evaluated by HF-PLM and DGT

Improvement of Advanced Sample Preparation Systems for the Determination of Trace Ni in Seawater by Electro-Membranes

Due to its important environmental role, the analysis of trace metals in natural waters is attracting increasing attention; consequently, faster and more accurate analytical methods are now needed to reach even lower limits of detection. In this work, we propose the use of electro-membrane extraction (EME) to improve analytical methods based on hollow fiber liquid phase micro-extraction (HFLPME). Specifically, an EME-based method for the determination of trace Ni in seawater has been developed, using an HFLPME system with di-2-ethylhexyl phosphoric acid (DEHPA) in kerosene as a chemical carrier, followed by instrumental determination by graphite furnace atomic absorption spectroscopy (GFAAS). Under optimum conditions, Ni was pre-concentrated 180 ± 17 times after 15 min, using sample pH = 5.5, the concentration of DEHPA 0.9 M in the liquid membranes, and 1.9 M HNO₃ in the acceptor solution, as well as an electric potential of 25 V with the sample being stirred at 500 rpm. When compared with other HFLPME systems for pre-concentration of trace Ni in seawater in the absence of electric potential, the enrichment factor was improved 2.2 times, while the time of extraction was reduced an 89%. The limit of detection of the new method was 23.3 ng L^-1, and both its applicability and accuracy were successfully evaluated by analyzing Ni concentration in a seawater-certified reference material (BCR-403), showing the reliability of EME for sample preparation in the determination of trace metals in marine water samples.

A Critical Study of the Effect of Polymeric Fibers on the Performance of Supported Liquid Membranes in Sample Microextraction for Metals Analysis

Popularity of hollow fiber-supported liquid membranes (HF-SLM) for liquid-phase microextraction (HF-LPME) has increased in the last decades. In particular, HF-SLM are applied for sample treatment in the determination and speciation of metals. Up to the date, optimization of preconcentration systems has been focused on chemical conditions. However, criteria about fiber selection are not reflected in published works. HFs differ in pore size, porosity, wall thickness, etc., which can affect efficiency and/or selectivity of chemical systems in extraction of metals. In this work, Ag+ transport using tri-isobutylphosphine sulfide (TIBPS) has been used as a model to evaluate differences in metal transport due to the properties of three different fibers. Accurel PP 50/280 fibers, with a higher effective surface and smaller wall thickness, showed the highest efficiency for metal transport. Accurel PP Q3/2 exhibited intermediate efficiency but easier handling and, finally, Accurel PP S6/2 fibers, with a higher wall thickness, offered poorer efficiency but the highest stability and capability for metal speciation. Summarizing, selection of the polymeric support of HF-SLM is a key factor in their applicability of LPME for metals in natural waters.

Assessing the uranium DGT-available fraction in model solutions

The uranium speciation in humic acid (HA) and fulvic acid (FA) model solutions was investigated by diffusive gradients in thin films (DGT). A reference solution was used to normalize the DGT data from different samples. This approach was used to assess uranium DGT-available fraction (F_U), which was calculated from experimental data and reflect both the mobility and lability of uranium species. F_U decreased with increasing HA or FA concentrations, because more uranium was able to bind the strong binding sites of HA or FA. When copper was spiked, F_U increased due to the competition between copper and uranium. In HA model solutions, an increase of ionic strength could increase F_U, and when pH was greater than 7, F_U increased significantly. The DGT uptake factor (φ), which can be obtained from data fitting, is the ratio of the product of diffusion coefficient and lability degree of the unknown sample to that of the reference solution. In U-HA-NaHCO₃ solutions, UO₂(CO₃)₂^2- had a relatively high φ value and might be the most DGT-available species. This approach allows the comparison of DGT data from different samples, and combining with a data fitting procedure, it can be used to investigate the distribution of metal species.

Selective solvent bar micro-extraction as a single-step approach for the measurement of Cu fractions in seawater

Hollow fibre-supported liquid membrane was used for Cu fractionation in marine waters, using di-2-pyridylketone benzoylhydrazone (dPKBH) as a carrier due to its capacity to transport dissolved inorganic Cu at natural seawater pH. Optimized conditions were dPKBH (0.5 mmol L^-1), HNO₃ (0.5 mol L^-1) as acceptor agent, extraction time of 120 min and stirring speed of 800 rpm. Additionally, the selectivity of the method for the extraction of the inorganic Cu fraction was validated by comparing the experimental results with theoretical data, and a mathematical model was obtained for estimation of Cu linked to dissolved organic matter. The method was applied for the measurement of Cu fractions in real seawater samples. Results were successfully compared with the reference material BCR 403 and recovery analysis in waters from the Gulf of Cádiz, showing that it could be used as a simple approach for the study of different Cu fractions in marine waters. Graphical abstract.

Trace metal speciation in North Sea coastal waters

Most trace metals exhibit a dual role in marine waters, acting as nutrients at low concentration and being toxic at high concentration. But besides concentration range, speciation is also an important factor. They both show both seasonal and spatial variations. A thorough comparison between total dissolved and particulate concentrations estimated from manual sampling and an assessment of the bioavailability using Diffusive Gradients in Thin Films (DGT) has been performed in this work for Cd, Co, Cu, Ni and Pb, at several sampling points of the Belgian Coastal Zone (BCZ). Additional information to trace back the origin and identify the anthropogenic fingerprint of Suspended Particulate Matter (SPM) was measured using stable carbon isotope measurements in particulate organic matter. Our results show that: (i) particulate and total dissolved metal concentrations are higher at two stations, one in the harbor of Oostende and one offshore; (ii) dissolved and particulate trace metal concentrations do not correlate with the dissolved labile fractions; and (iii) SPM in the harbor zone is likely from allochthonous sources, while in the offshore station marine origin has been evidenced. Our results indicate that, even though contamination is higher in the harbor zones, the trace metal toxicity, which is linked to the metal bioavailability, is most likely not higher than in the open sea. However, with increasing acidification of the ocean, a shift from particulate to dissolved phase might lead to increasing adverse effects on the coastal environment.

Selective ionic liquid solvent bar micro-extraction for estimation of ultra-trace silver fractions in marine waters

Ag can be found in the ocean at the ultra-trace level, mainly as AgCl_n^(n-1)- and complexed by dissolved organic matter (Ag-DOM). However, methods for studying Ag speciation in marine waters are limited by the lack of extractants capable to separate organic and inorganic silver species in natural conditions of seawater samples. In this work, a two-phase solvent bar micro-extraction method using the ionic liquid trihexyltetradecylphosphonium chloride (Cyphos® 101) was applied for selective micro-extraction of AgCl_n^(n-1)- from organic silver in marine waters, working at seawater pH,. The application to real samples was performed under the following conditions: 2.5% Cyphos® 101 in kerosene solution with 10% dodecan-1-ol inside the fiber, and 30 min of sample extraction at a stirring rate of 800 rpm. The proposed SBME was successfully used for estimation of Ag fractions in waters from the Bay of Cádiz (South-west Spain) showing its applicability for a simple, fast and environmentally friendly speciation of silver in marine water samples. The method presented a linear response up to 500 ng L^-1 and a detection limit of 0.4 ng L^-1, using GF-AAS for instrumental determination.

Polymer inclusion membrane to access Zn speciation: Comparison with root uptake

Metal speciation studies can be performed with a new technique based on a functionalized membrane. The estimation of not only the total amount of metal, but also the metal available to living organisms is very important. In this context, we have investigated the use of a polymer inclusion membrane (PIM) in a new tool for the determination of free metal ion concentration. In order to check the usefulness of PIM devices in metal speciation studies and metal availability to potato plants (Solanum tuberosum), Zn has been chosen as a case study. The PIM designed for Zn transport uses polyvinyl chloride (PVC) as polymer and di-(2-ethylhexyl) phosphoric acid (D2EHPA) as carrier, with 0.01M nitric acid in the receiving solution. The stability of the PIM has been demonstrated and good linearity of PIM-device fluxes (J_PIM) with free metal concentration was observed for total metal concentrations ranging from 3μM up to 70μM. The presence of different ligands, such as ethylenediaminetetraacetic acid (EDTA), humic acid (HA) and citrate, greatly influences the measured J_PIM because the formation of metal complexes in the donor phase decreases the free Zn concentration in the sample. Good correlation has been found when comparing PIM fluxes and metal accumulation in potato plants roots in the presence of EDTA. But, the root uptake did not change when adding citrate and HA to the hydroponic medium, so the uptake does not always follows the Free Ion Activity Model (FIAM). These ligands might induce physiological changes in the roots and enhance metal uptake.

Ionic liquid solvent bar micro-extraction of CdCln(n-2)- species for ultra-trace Cd determination in seawater

Water analysis of trace metals has been benefited by recent studies on sample preparation by liquid micro-extraction. However, there are still limitations for its application to seawater, such as the need of additives to preserve the sample or the availability of chemical extractants for the selective extraction from highly saline samples. In this work, a three phase solvent bar micro-extraction (3SBME) system containing the ionic liquid trioctylmethylammonium chloride (Aliquat^® 336) has been used for isolation and pre-concentration of Cd from seawater samples, due to its ability for ionic exchange of CdCl_n^(n-2)-. The system was optimized to work at the natural pH of seawater, and conditions for application to real samples were 0.18 M Aliquat^® 336 dissolved in kerosene with 0.25 M dodecan-1-ol as organic solution, 1.5 M HNO₃ as acceptor solution, 60 min extraction time, and 800 rpm stirring speed in the sample. Loss of organic solution into the sample during extraction was evaluated and revealed its dependence on stirring rate and extraction time. Under optimum conditions samples containing Cd 0.09-0.90 nM were pre-concentrated 65 times. GF-AAS was used for metal quantification with a limit of detection of 0.04 nM. Accuracy was successfully evaluated measuring Cd in a seawater certified reference material BCR-403.

Assessing cadmium and vanadium accumulation using diffusive gradient in thin-films (DGT) and phytoplankton in the Churchill River estuary, Manitoba

Diffusive gradient in thin films (DGT) and phytoplankton communities were evaluated for the measurement of Cd and V at environmentally relevant concentrations in laboratory settings and in the Churchill River estuary (Manitoba, Canada) during an annual spring melt. Despite rapid changes in hydrology and water quality, DGT samplers and intracellular Cd and V concentrations were positively correlated (0.79 < r(2) < 0.99), suggesting comparable accumulation trends between both DGT-labile and intracellular monitoring techniques. The largest accumulated concentrations of both Cd and V by DGT and phytoplankton accumulation methods were found later into the river discharge period. In controlled settings, accumulated Cd and V concentrations by the diatom Attheya septentrionalis displayed a strong correlation with metals accumulated by DGTs (r(2) > 0.99). Principal component analysis (PCA) reinforced similarities between both metal monitoring techniques and assessed how changing environmental variables during the river discharge period influenced each monitoring technique. Cd accumulation was influenced by DOC concentrations and protein-like DOM whereas ionic strength (i.e. conductivity) and humic-like DOM influenced V accumulation. The present findings suggest that (1) DGT is a versatile tool for monitoring bioaccumulation of Cd and V in highly dynamic environmental systems and (2) DOC concentration, DOM composition, conductivity, pH, and river discharge influence the bioavailability of Cd and V in estuarine and riverine waters.

Solvent bar micro-extraction with graphite atomic absorption spectrometry for the determination of silver in ocean water

Main drawbacks for silver determination in seawater are the effects of samples matrix and that Ag appears in the sub ng L(-1). Available methods for sample preparation in Ag analysis are based on solid and liquid extraction using tedious process that increase the cost of analysis and the risk of sample contamination, producing important waste amounts. Solvent bar micro-extraction (SBME) allows the pre-concentration of Ag in a micro-volume of the ionic liquid Aliquat 336® in kerosene solution. For this reason, it is considered as a green alternative to standard methods. The method has been optimized using synthetic seawater samples, offering the highest response for samples at pH=2, using 5% Aliquat 336® dissolved in kerosene containing 5% dodecan-1-ol as acceptor solution and after 1h stirring at 800rpm. The method exhibited linearity up to 50ngL(-1), with a limit of detection of 0.09ngL(-1), covering the concentration range of interest for environmental studies. Finally, it was applied for determination of Ag in real seawater samples, and the results were compared with the reference method of liquid-liquid extraction with 1-pyrrolidine-dithiocarbamate and diethylammonium-diethyldithiocarbamate, showing the applicability of ionic liquid based SBME using Aliquat 336(®) for the simple monitoring of silver ultra-traces in seawater analysis.

Statistical evaluation of biogeochemical variables affecting spatiotemporal distributions of multiple free metal ion concentrations in an urban estuary

Free metal ion concentrations have been recognized as a better indicator of metal bioavailability in aquatic environments than total dissolved metal concentrations. However, our understanding of the determinants of free ion concentrations, especially in a metal mixture, is limited, due to underexplored techniques for measuring multiple free metal ions simultaneously. In this work, we performed statistical analyses on a large dataset containing repeated measurements of free ion concentrations of Cu, Zn, Pb, Ni, and Cd, the most commonly measured metals in seawater, at five inshore locations in Boston Harbor, previously collected using an in-situ equilibrium-based multi-metal free ion sampler, the 'Gellyfish'. We examined correlations among these five metals by season, and evaluated effects of 10 biogeochemical variables on free ion concentrations over time and location through multivariate regressions. We also explored potential clustering among the five metals through a principal component analysis. We found significant correlations among metals, with varying patterns over season. Our regression results suggest that instead of dissolved metals, pH, salinity, temperature and rainfall were the most significant determinants of free metal ion concentrations. For example, a one-unit decrease in pH was associated with a 2.2 (Cd) to 99 (Cu) times increase in free ion concentrations. This work is among the first to reveal key contributors to spatiotemporal variations in free ion concentrations, and demonstrated the usefulness of the Gellyfish sampler in routine sampling of free ions within metal mixtures and in generating data for statistical analyses.

In situ evaluation of DGT techniques for measurement of trace metals in estuarine waters: a comparison of four binding layers with open and restricted diffusive layers

Four different DGT binding layers were used to make selective measurements of trace metals in coastal waters within The Broadwater (Gold Coast, Queensland). Chelex and PAMPAA (polyacrylamide-polyacrylic acid) binding layers were used to measure cations (Cd, Co, Cu, Mn, Ni, Pb, Zn), and Metsorb was used to measure anions (Al, As, Mo, Sb, V, W). A mixed binding layer (MBL) containing both Chelex and Metsorb was used to measure each of the trace metals and determine diffusive boundary layer (DBL) thicknesses. DGT measurements that were not corrected for the DBL thickness (0.049-0.087) were underestimated by 70% on average. Good agreement was observed between DGT-MBL and DGT-Chelex for measurement of Cd, Co, Cu, Ni, Pb and Zn, and between DGT-MBL and DGT-Metsorb for As, Sb and V. DGT-MBL measured significantly higher concentrations for Mn (compared with DGT-Chelex) and Al (compared with DGT-Metsorb). DGT-Chelex measured only 6-8% of Al species measured by either DGT-MBL or DGT-Metsorb. DGT-PAMPAA measurements of Cu, Pb and Al were lower than those of either DGT-MBL or DGT-Chelex varying from 74-81% for Cu to 54-70% for Pb and 51-55% for anionic Al(OH)4(-), suggesting that this binding layer may make more selective measurements. All measured trace metal concentrations were well below ANZECC water quality guidelines, except for Cu which was 2 to 10 times higher than trigger values. Each of the DGT techniques was deployed using both open and restricted diffusive layers (ODL and RDL). Most trace metal measurements were not significantly different with ODL and RDL for all binding layers. However, concentrations of Cu (CRDL/CODL = 0.68-0.75) and Al (CRDL/CODL = 0.73-0.79) were significantly different with DGT-MBL, DGT-Chelex and DGT-Metsorb.

Evaluation of the measurement of Cu(II) bioavailability in complex aqueous media using a hollow-fiber supported liquid membrane device (HFSLM) and two microalgae species (Pseudokirchneriella subcapitata and Scenedesmus acutus)

The environmental bioavailability of copper was determined using a hollow-fiber supported liquid membrane (HFSLM) device as a chemical surrogate and two microalgae species (Scenedesmus acutus and Pseudokirchneriella subcapitata). Several experimental conditions were studied: pH, the presence of organic matter, inorganic anions, and concomitant cations. The results indicated a strong relationship between the response given by the HFSLM and the microalgae species with free copper concentrations measured by an ion selective electrode (ISE), in accordance with the free-ion activity model (FIAM). A significant positive correlation was evident when comparing the bioavailability results measured by the HFSLM and the S. acutus microalga species, showing that the synthetic device may emulate biological uptake and, consequently, be used as a chemical test for bioavailability measurements using this alga as a biological reference.

Dissolved trace metal speciation in estuarine and coastal waters: comparison of WHAM/Model VII predictions with analytical results

The authors apply the chemical speciation model WHAM/Model VII to investigate the distribution of metal species of Fe(III) and the divalent cations of Ni, Cu, Zn, Cd, Hg, and Pb, in the water column of estuaries and coastal areas. The authors compare, for the same locations, measured and modeled free ion and organically bound metal concentrations. The modeled free ion calculations show varying levels of agreement with experimental measurements. Where only natural organic matter is considered as the organic ligand, for Ni, Cd, and Pb, agreement within 1 order of magnitude is found in 122 of 128 comparisons. For Fe and Zn comparisons 12 of 34 (Fe) and 10 of 18 (Zn) agree to within 1 order of magnitude, the remaining modeled values being over 1 order of magnitude higher than measurements. Copper measurements agree within 1 order of magnitude of modeled values in 314 of 533 (59%) cases and are more than 1 order of magnitude lower than modeled values in 202 cases. There is a general tendency for agreement between modeled and measured values to improve with increasing total metal concentrations. There are substantial variations among different analysis techniques but no systematic bias from the model is observed across techniques. It would be beneficial to cross-validate the different analytical methods, in combination with further modeling. The authors also assessed the effect of including an anthropogenic organic ligand (ethylenediamine tetraacetic acid (EDTA)) in the modeling, given its known presence in some coastal environments. Except for Cd, all metals were sensitive to the presence of EDTA, even at a low concentration of 50 nM.

Passive sampling methods for contaminated sediments: state of the science for metals

"Dissolved" concentrations of contaminants in sediment porewater (Cfree ) provide a more relevant exposure metric for risk assessment than do total concentrations. Passive sampling methods (PSMs) for estimating Cfree offer the potential for cost-efficient and accurate in situ characterization of Cfree for inorganic sediment contaminants. In contrast to the PSMs validated and applied for organic contaminants, the various passive sampling devices developed for metals, metalloids, and some nonmetals (collectively termed "metals") have been exploited to a limited extent, despite recognized advantages that include low detection limits, detection of time-averaged trends, high spatial resolution, information about dissolved metal speciation, and the ability to capture episodic events and cyclic changes that may be missed by occasional grab sampling. We summarize the PSM approaches for assessing metal toxicity to, and bioaccumulation by, sediment-dwelling biota, including the recognized advantages and limitations of each approach, the need for standardization, and further work needed to facilitate broader acceptance and application of PSM-derived information by decision makers.

Combined use of DGT and transplanted shrimp (Litopenaeus vannamei) to assess the bioavailable metals of complex contamination: implications for implementing bioavailability-based water quality criteria

The diffusive gradients in thin films (DGT) were field deployed alongside the shrimp Litopenaeus vannamei at seven sites with different levels of contamination to assess the potentially bioavailable and toxic fraction of metal contaminants. After 7 days of exposure, several antioxidant biomarkers were quantified in hepatopancreas of exposed shrimps, and tissue levels as well as the total, dissolved, and DGT-labile concentrations of metal contaminants were determined in the pooled site samples. The results showed that the caged shrimps had high tissue contaminant concentrations and significantly inhibited antioxidant responses at the more contaminated sites. DGT-labile metal concentrations provided better spatial resolution of differences in metal contamination when compared with traditional bottle sampling and transplanted shrimp. The total, dissolved, and DGT-labile metal fractions were used to evaluate the potential bioavailability of metal contaminants, comparing with metal accumulation and further linking to antioxidant biomarker responses in tissues of exposed shrimps. Regression analysis showed the significant correlations between DGT-Cu concentrations and tissue-Cu and activities of some biomarker responses in the shrimp hepatopancreas. This indicated that DGT-labile Cu concentrations provided the better prediction of produced biological effects and of the bioavailability than the total or dissolved concentrations. The study supports the use of methods combining transplanted organisms and passive sampling for assessing the chemical and ecotoxicological status of aqueous environments and demonstrates the capability of the DGT technique as a powerful tool for measuring the bioavailability-based water quality in variable coastal environments.

Tolerance of polar phytoplankton communities to metals

Large amounts of pollutants reach polar regions, particularly the Arctic, impacting their communities. In this study we analyzed the toxic levels of Hg, Cd and Pb to natural phytoplankton communities of the Arctic and Southern Oceans, and compared their sensitivities with those observed on phytoplankton natural communities from temperate areas. Mercury was the most toxic metal for both Arctic and Antarctic communities, while both Cd and Pb were toxic only for the Antarctic phytoplankton. Total cell abundance of the populations forming the Arctic community increased under high Cd and Pb concentrations, probably due to a decrease of the grazing pressure or the increase of the most resistant species, although analysis of individual cells indicated that cell death was already induced at the highest levels. These results suggest that phytoplankton may have acquired adapting mechanisms to face high levels of Pb and Cd in the Arctic Ocean.

Effects of nitrate addition and iron speciation on trace element transfer in coastal food webs under phosphate and iron enrichment

Coastal organisms are often exposed to both iron enrichment and eutrophication. Trace elements transfer in coastal food webs are critical for marine life and therefore influence coastal ecosystem function and the global carbon cycle. However, how these exposures affect algal element uptake and the subsequent element transfer to marine copepods (Tigriopus japonicus) is unknown. Here we investigated the effects of nitrate addition and iron speciation (Fe (OH)3 or EDTA-Fe) on the biological uptake of Cu, Zn, and Se under phosphate and iron enrichment, using Thalassiosira weissflogii, Skeletonema costatum, and Chlorella vulgaris as model marine algae. Algal element adsorption/absorption generally increased with increasing macronutrient concentrations. Algal element assimilation efficiencies depended on iron speciation and marine algae species. Element assimilation efficiencies of copepods were significantly correlated to the intracellular element concentrations in algal cells. Element uptake and transfer were controlled by eutrophication, iron speciation, and algal species in coastal food webs.

Effects of Cd, Cu, Ni, and Zn on brown tide alga Aureococcus anophagefferens growth and metal accumulation

Trace metals play important roles in regulating phytoplankton growth and could influence algal bloom development. Laboratory studies were conducted to evaluate the influence of environmentally relevant concentrations of Cd, Cu, Ni, and Zn on Aureococcus anophagefferens bloom (brown tide) development. Results show that the elevated Ni(2+) concentrations, e.g. those of brown tide waters in the northeastern US, greatly stimulated A. anophagefferens growth (as compared to the control without Ni addition), yet, only low amounts of dissolved Ni were sequestered, thus leaving excessive Ni directly promoting A. anophagefferens blooms. The medium effective concentration EC(50) (Me(2+)) suggests A. anophagefferens has similar Cd sensitivity but much greater Cu tolerance as compared to cyanobacteria, as such, excessive Cu could indirectly promote A. anophagefferens blooms by inhibiting competitors such as Synechococcus sp. The effects of Ni and Cu promoting growth are consistent with the recent genomic study of this alga. In addition, Zn(2+) concentrations lower than those in brown tide waters enhance A. anophagefferens growth, but Zn sequestration in A. anophagefferens would not substantially reduce total dissolved Zn in these waters. Overall, this study, showing that excessive Cu and Ni likely promote brown tides, provides evidence for trace metal linkages in algal bloom development.

Assessing contaminated sediments in the context of multiple stressors

Sediments have a major role in ecosystem functioning but can also act as physical or chemical stressors. Anthropogenic activities may change the chemical constituency of sediments and the rate, frequency, and extent of sediment transport, deposition, and resuspension. The importance of sediments as stressors will depend on site ecosystem attributes and the magnitude and preponderance of co-occurring stressors. Contaminants are usually of greater ecological consequence in human-modified, depositional environments, where other anthropogenic stressors often co-occur. Risk assessments and restoration strategies should better consider the role of chemical contamination in the context of multiple stressors. There have been numerous advances in the temporal and spatial characterization of stressor exposures and quantification of biological responses. Contaminated sediments causing biological impairment tend to be patchy, whereas more pervasive anthropogenic stressors, such as alterations to habitat and flow, physical disturbance, and nutrient addition, may drive large-scale ecosystem responses. A systematic assessment of relevant ecosystem attributes and reference conditions can assist in understanding the importance of sediments in the context of other stressors. Experimental manipulations then allow for the controlled study of dominant stressors and the establishment of causal links. This approach will result in more effective management of watersheds and waterways.

3-Ethyl-4-(p-chlorobenzylidenamino-4,5-dihydro-1H-1,2,4-triazol-5-one (EPHBAT) as precipitant for carrier element free coprecipitation and speciation of chromium(III) and chromium(VI)

A method for the separation and speciative determination of Cr(VI) and Cr(III) has been developed. The procedure is based on coprecipitation of Cr(III) on 3-ethyl-4-(p-chlorobenzylidenamino-4,5-dihydro-1H-1,2,4-triazol-5-one (EPHBAT) without carrier element. The Cr(III) can be selectively precipitated on EPHBAT in the pH range of 8.0-9.0, while Cr(VI) cannot be retained. Total chromium was determined after the reduction of Cr(VI) to Cr(III) with 0.5 mL of concentrated H2SO4 and 0.5 mL of ethanol. Cr(VI) concentrations were obtained as the respective differences between total chromium and Cr(III). Experiments were performed to optimize conditions, such as pH, amounts of EPHBAT, sample volume, etc. A preconcentration factor of 50-fold was achieved for Cr(III). The detection limit of the method for Cr(III) was 1.0 microg L(-1). To validate the developed method, the certified reference materials (NIST SRM 1573a and GBW 0703) were analyzed. The method was applied for the speciation of chromium in spiked natural water samples with satisfactory results.