Metals In Natural Waters Research Articles

Tris buffer-accelerated ligand exchange rate for instant fluorescence detection of trivalent chromium ion

Functional nucleic acids (FNAs) have attracted a lot of attention for the rapid detection of metal ions. Cr3+ is one of the major heavy metal ions in natural waters. Due to the slow ligand exchange rate of Cr3+, the FNA-based Cr3+ sensors require long assay times, limiting the on-site applications. In this study, we report that the good's buffers containing amino and polyhydroxy groups greatly increase the ligand exchange rate of Cr3+. Using EDTA as a model coordinate ligand, the Tris buffer (100 mM, pH 7.0) showed the best acceleration effect among the eight buffers. It improved the rate constant ∼20-fold, shorten the half-time 19-fold, and lowered the activation energy ∼70% at 40 °C. The Tris buffer was then applied for sensor based on the Cr3+-binding induced fluorescence quenching of fluorescein (FAM)-labeled and single-stranded DNA (ssDNA), which shortened the assay time from 1 h to 1 min. The Tris buffer also ∼100% enhanced the fluorescence intensity of FAM, achieving the 11.4-fold lower limit of detection (LOD = 6.97 nM, S/N = 3). By the combination use of the Tris buffer and ascorbic acid, the strong interference from Cu2+, Pb2+, and Fe3+ suffered in many previous reported Cr3+ sensors was avoided. The practical application of the sensor for the detection of Cr3+ spiked in the real water samples were demonstrated with high recovery percentages. The Tris buffer could be applied for other metal ions with slow ligand exchange rate (such as V2+, Co3+ and Fe2+) to solve diverse issues such as long assay time and low synthesis yield of metal complexes, without the need of heating treatment.

Adsorption of Heavy Metals on Alkali-Activated Zeolite Foams.

Elevated concentrations of heavy metals in natural waters can cause significant ecological problems. It is therefore essential to ensure their removal from any water discharged into the environment immediately, especially in case of an accident, where there is a risk of releasing large quantities or high concentrations. The aim of this paper is to test a newly developed adsorbent for the removal of heavy metals from aqueous solutions-in particular, it is very fast adsorption, and thus efficiency, during clean-ups. The alkali-activated foamed zeolite adsorbent was laboratory-prepared and -tested in both batch and flow-through arrangements on single and multi-component solutions and compared with natural zeolite. The experimental setup for batch adsorption consisted of a set of samples and solutions containing iron, cobalt, manganese, zinc and nickel. The samples were put on a horizontal shaker with a 500 mg adsorbent loading in a 50 mL solution. The column adsorption experimental setup consisted of a glass column with an inside diameter of 15 mm and a bed length of 165 mm. A measured amount of each adsorbent was added to the column to achieve a filter fixed-bed height of 160 mm. The high efficiency of the tested adsorbent on various heavy metals was confirmed. The adsorbent has a high potential for use in decontamination processes, water protection and landscape revitalization. Due to its rapid precipitation and subsequent fixation of metal cations in the form of insoluble oxide or hydroxide, it can be used as an emergency adsorbent, the great advantage of which is its low production cost and natural origin.

Preparation and Characterization of Iron Oxide Nano-adsorbent by Enteromorpha Flexuosa Algae obtained from Yanbu Red Sea, Saudi Arabia

Water contamination caused by toxic cadmium metal ions is a worldwide problem. There is a need to explore new methods of cadmium removal from water. The green algae Enteromorpha flexuosa, obtained from the Red Sea in Yanbu, Saudi Arabia, was used to prepare iron nanoparticles. TEM, FT-IR, XRD, and SEM techniques were used to characterize the prepared nanoparticles. The prepared nanoparticle's surface was rough, with nanoparticle sizes ranging from 10 to 50 nm. The developed nanoparticles were used to adsorb cadmium ions from water in batch mode. With a 25.0 µg/L concentration, a temperature of 25˚C, 7.0 pH, 60 minutes contact time and 0.5 g/L dose, the maximum removal of cadmium was 48.2 µg/g. The sorption efficiency was measured using the Dubinin-Radushkevich, Temkin, Langmuir and Freundlich models. The amounts of ΔG° were -8.0, -9.93 and -12.24 kJ/mol while the values of ΔS° and ΔH° were -30.96 x 10-3 kJ/mol and 37.79 x 10-2 kJ/mol. These data confirmed the endothermic nature of cadmium metal ions removal. Along with the liquid film diffusion process, the adsorption adopted the kinetics of pseudo-second-order type. The recorded adsorption method is fast, cost-effective, and environmentally friendly and can be applied for testing the elimination of cadmium metal ions in natural waters.

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.

Ferrozine colorimetry and reverse flow injection analysis (rFIA) based method for the determination of total iron in aqueous solutions at nanomolar concentrations

Iron is one of the most microbiologically and chemically important metals in natural waters. The biogeochemical cycling of iron is significantly influenced by the redox cycling of Fe(II) and Fe(III). Because of the unique chemistry of iron, it is often needed to analyze iron at nano-molar concentrations. This article describes a reverse flow injection analysis (rFIA) based method with ferrozine spectrophotometric detection to quantify total iron concentration in stream water at nanomolar concentrations. The rFIA system has a 0.65 nM detection limit and a linear dynamic range up to 1.40 μM for the total iron analysis. The detection limit was achieved using a 1.0 m long liquid waveguide capillary flow cell, 1.50 m long knotted reaction coil, 87.50 μL injection loop and a miniature fiber optics spectrophotometer. The optimized colorimetric reagent has 1.0 mM ferrozine, 0.1 M ascorbic acid, 1.0 mM citric acid and 0.10 M acetate buffer adjusted to pH 4.0. The best sample flow rate is 2.1 mL min−1 providing a sample throughput of more than 15 samples h−1. The linear dynamic range of the method can be adjusted by changing the volume of the injection loop. The rFIA manifold was assembled exclusively from commercially available components.

Spectrophotometric Determination of Fe(II) and Fe(III) Using 5-(4-Ethylphenyl azo ) 2-Hydroxybenzaldehyde Oxime Reagent

Spectrophotometric Determination of Fe(II) and Fe(III) Using 5-(4-Ethylphenyl azo ) 2-Hydroxybenzaldehyde Oxime Reagent

Determination of Background Concentrations of Ag, Pd, Pt and Au in Highly Mineralized Ground Waters at Sub-ng L-1 Concentrations by Online Matrix Separation/Pre-Concentration Coupled to ICP-SFMS.

Though not regulated in directives such as the Water Framework Directive of the European Union, the investigation of geogenic background concentrations of certain elements such as precious metals is of increasing interest, in particular for the early detection of a potential environmental pollution due to the increased use in various industrial and technological applications and in medicine. However, the precise and accurate quantification of precious metals in natural waters is challenging due to the complex matrices and the ultra-low concentrations in the (sub-) ng L−1 range. A methodological approach, based on matrix separation and pre-concentration on the strong anion exchange resin TEVA® Resin in an online mode directly coupled to ICP-SFMS, has been developed for the determination of Ag, Pt, Pd and Au in ground water. Membrane desolvation sample introduction was used to reduce oxide-based spectral interferences, which complicate the quantification of these metals with high accuracy. To overcome errors arising from matrix effects—in particular, the highly varying major ion composition of the investigated ground water samples—an isotope dilution analysis and quantification based on standard additions, respectively, were performed. The method allowed to process four samples per hour in a fully automated mode. With a sample volume of only 8 mL, enrichment factors of 6–9 could be achieved, yielding detection limits <1 ng L−1. Validation of the trueness was performed based on the reference samples. This method has been used for the analysis of the total concentrations of Ag, Pt, Pd and Au in highly mineralized ground waters collected from springs located in important geological fault zones of Austria’s territory. Concentrations ranges of 0.21–64.2 ng L−1 for Ag, 0.65–6.26 ng L−1 for Pd, 0.07–1.55 ng L−1 for Pt and 0.26–1.95 ng L−1 for Au were found.

Determination of ambient dissolved metal ligand complexation parameters via kinetics and pseudo-voltammetry experiments

Dissolved chemical speciation of metals in natural waters encompasses a wide range of inorganic and organic compounds including metal organic ligand complexes, ML. Because of the different filters used, “dissolved” speciation can range from simple metal-ligand complexes with an average size of about 0.66 nm (mass of <3 k-daltons) to nanoparticles of 1 to 100 nm to colloidal forms that are 10 to 200–400 nm in size. Strong metal-ligand, ML, complexes are normally considered to be in <1 nm size fraction. Over the last 3 decades, competitive ligand exchange – cathodic stripping voltammetry (CLE-CSV) titrations have been the method of choice to study complexation. These titrations primarily give information on the excess ligands in the sample rather than the actual ligand in MLunknown complexes because they require adding metal to the sample. Thus, metal-ligand CLE-CSV titrations do not provide much information on the actual ligand present in MLunknown. However, pseudovoltammetry provides the thermodynamic stability constant, Ktherm, for Zn, Cu, Cd and Pb as the MLunknown complex is destroyed by reduction at the Hg electrode to form metal(Hg). Pseudovoltammetry does not require the addition of any reagents to the sample, but cannot be performed for ions such as Fe(III) [and Mn(III)] because reduction of the ion results in the reduction of the metal ion in the complex without destroying MLunknown. For these ions, kinetic experiments to recover the metal in the ML complex can provide information on the MLunknown dissociation rate constant, kd, and the conditional equilibrium constant, KcondML′. In these kinetic experiments, a competitive ligand (Lcomp) is added to the sample, and over time the MLcomp complex is measured by CSV. If all the metal in MLunknown is recovered, kd of MLunknown can be determined. If only a portion of the metal in MLunknown is recovered, equilibrium is achieved and KcondML′ as well as kd can be determined in a single experiment; kf can then be calculated. We describe how these methods can be used to determine information on the actual MLunknown complex. We show that 7 thermodynamic, kinetic and speciation parameters (Ktherm, KcondML′, KcondM′L′, kf, kd, αM′, αL′) for MLunknown complexes can be derived from a combination of two of these experiments. The approaches described here are useful to determine these parameters for known ML complexes once a ligand has been isolated by advanced separation methods (e.g., LC-MS) and reacted with a metal of interest.

Biosorción de Cu(II) sobre cáscaras de maní y maltas residuales. Incorporación de la biomasa contaminada en matrices cerámicas

La presencia de metales pesados en los cursos naturales de agua, tiene efectos nocivos sobre la salud de muchas especies biológicas y sobre el medio ambiente. Los biosorbentes son ampliamente reconocidos como adsorbentes de bajo costo porque son abundantes en la naturaleza o por ser materiales de desecho de la agroindustria. En el presente trabajo se estudia la remoción de iones de Cu (II) en solución acuosa, utilizando cáscaras de maní y residuos de cebada de la producción de cerveza como materiales adsorbentes. Además se plantea la posibilidad de inmovilizar el metal contaminante junto a la biomasa en matrices cerámicas, comenzando por el estudio de la temperatura óptima de cocción. Se realizó una exhaustiva caracterización de ambas biomasas, y se analizaron numerosas variables en el proceso de biosorción en búsqueda de condiciones que maximicen la capacidad adsorbente de las mismas. Los resultados muestran que las cáscaras de maní logran remociones de hasta el 40% del metal, mientras que los residuos de cebada no logran superar el 2,3% de remoción. En base a los resultados obtenidos y dado que ambas biomasas son un subproducto industrial abundante y de bajo costo, se sugiere a la biosorción mediante cáscaras de maní como un proceso efectivo y económico para la remoción de iones de cobre en aguas contaminadas. A su vez, se establecen temperaturas de 950°C-1000ºC como rango óptimo de cocción de las matrices cerámicas, para analizar la inmovilización de los metales removidos.

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.

Simultaneous IСP-MS determination of trace metals in natural water and snow after their preconcentration on novel adsorbent based on Al2O3 impregnated with Alizarin Complexone

ABSTRACTA simple and available method for on-line preparation of the adsorbent and solid phase extraction procedure for multi-element determination by inductively coupled plasma mass spectrometry (ICP-MS) has been proposed. The adsorbent (Al2O3-PB-AC) was synthesised by sequential impregnation of Al2O3 with Polybrene (PB) and Alizarin Complexone (AC). Cd(II), Cr(III), Ni(II), Pb(II) and Zn(II) were quantitatively recovered using Al2O3-PВ-AC from aqueous solutions at pH 6.5 and at a flow rate of 1.0 mL min−1. All the elements can easily be eluted by 3.0 mL 0.5 M HNO3. A mini-column packed with 0.100 g Al2O3-PB-AC retained all elements quantitatively from up to 50 mL multi-element solution with an enrichment factor of 16.7. The relative standard deviation for five replicate determinations was 3.5%, 7.3%, 6.2%, 7.4% and 4.7% for Cd(II), Cr(III), Ni(II), Pb(II) and Zn(II), respectively, for determination of 5 μg L−1 level. The developed method was applied for SPE-ICP-MS determination of Cd, Cr, Ni, Pb, Zn in snow and river waters.

Investigation of Complex Formation Process of Copper with Macromolecular Organic Substances, Isolated from Natural Waters

Natural macromolecular organic substances-fulvic acids take an active part in complex formation processes and stipulate migration forms of heavy metals in natural waters The calculation of the migration forms of heavy metals is one of the problematic issue of the contemporary chemistry, which couldn’t be solved without using the conditional stability constants of fulvate complexes. In spite of researches, experimental data on stability constants of complex compounds of fulvic acids with heavy metals ( among them copper) are heterogeneous and they differ in several lines from each other. One of the reason of such condition is ignoring an average molecular weight of the associates of fulvic acids, which finally causes the wrong results. Complex formation process between copper (II) and fulvic acids was studied by the solubility method at pH=9.0. Cu(OH)2 suspension was used as a solid phase. Fulvic acids were isolated from Paravani lake by the adsorption –chromatographic method. In this article is shown that, during complex formation process every 1/4 part of an associate of fulvic acids(Mw=7610), inculcates into copper's inner coordination sphere as an integral ligand, so it may assume, that the average molecular weight of the associate of fulvic acids which takes part in complex formation process equals to 1903. This part of the associate of fulvic acids was conventionally called an“active associate".The average molecular weight of the“active associate”was used for determination the composition of copper fulvate complex, the concentration of free ligand and stability constant, which equals to 2,25x107

Isolation of forms toxic metals in natural waters by ion exchange method

To study the forms of finding toxic microelements in natural waters, a technique using ion-exchange resins has been developed; KU-2 cation exchanger and AV-17 anion exchanger. Ionites with a grain size of 50–100 mesh were converted into H+ and Cl-forms by treatment with HCl, followed by washing with deionized water.

Modeling Water Pollution under Different Scenarios of Zinc Load on the Nizhnekamskoe Reservoir Watershed

The potentialities of the physically-based model ECOMAG-HM for the study of zinc content formation regularities in the Nizhnekamskoe Reservoir basin have been demonstrated. The basin is characterized by high concentrations of heavy metals in natural waters due to the significant content of ore-forming elements in rocks and a high level of economic development. The daily zinc concentrations have been calculated, and the maps of mean annual zinc concentrations in the river network have been compiled. Local areas of the catchment not covered by hydrochemical observations and showing a significant level of river water contamination by zinc have been identified. The fields of the genetic components of zinc hydrochemical runoff have been calculated. The contribution of anthropogenic sources to the zinc runoff formation has been estimated, and it has been established that, with the current level of anthropogenic load, the contribution of wastewater point discharges does not exceed 4%. The scenarios and consequences of increasing the amount of zinc discharged as part of wastewater are considered. The time scale of the catchment self-purification from zinc has been evaluated. The results show that, in the absence of external impacts on the catchment area, a decrease in zinc content in river waters over a 400-year period will be about as little as 8%.

Determination of Metals in Natural Waters by Inductively Coupled Plasma Optical Emission Spectroscopy after Preconcentration on Silica Sequentially Coated with Layers of Polyhexamethylene Guanidinium and Sulphonated Nitrosonaphthols.

A series of complexing adsorbents is prepared by coating silica particles with linear polyhexamethylene guanidinium (PHMG) chloride followed by saturation with a number of sulphonated nitrosonaphthols reagents electrostatically retained by positively charged polymer layer. PHMG coated silica is hydrolytically stable even during treatment with 6 M HCl heated up to 50 °C. The adsorption of 1-nitroso-2-naphthol-3,6-disulfonic acid (nitroso-R-salt), 2-nitroso-1-naphthol-4-sulfonic acid (nitroso-N-salt), and 2-nitroso-1-naphthol-3,6-disulfonic acid (nitroso-K-salt) on PHMG modified silica was studied. The effective immobilisation of sulphonated nitrosonaphthols was achieved in the range of pH of 3 - 8, while the adsorption of the monosulphonated reagent (nitroso-N-salt) is twice as high as the disulphonated analogues (nitroso-R-salt and nitroso-K-salt). The adsorption of Cu(II), Fe(III), Co(II), Ni(II), Al(III), Zn(II), Pb(II), Mn(II), and Cr(III) on prepared complexing adsorbents under static and dynamic conditions was studied as a function of time, pH, sample volume, and presence of interfering ions. Metal ions can be desorbed by using 1 M HCl or 1 M HNO3. The preconcentration factors of metals under optimized conditions are varied from 20 to 80. The developed method was used for the preconcentration of trace metals from natural waters followed by ICP-OES determination. The sub-ppb limits of detection of metals are achieved.

Synthesis of MnCo2O4 nanoparticles as modifiers for simultaneous determination of Pb(II) and Cd(II)

The porous spinel oxide nanoparticles, MnCo2O4, were synthesized by citrate gel combustion technique. Morphology, crystallinity and Co/Mn content of modified electrode was characterized and determined by Fourier transform infra-red spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction pattern analysis (XRD), simultaneous thermogravimetry and differential thermal analysis (TG/DTA). Nanoparticles were used for modification of glassy carbon electrode (GCE) and new sensor was applied for simultaneous determination of Pb(II) and Cd(II) ions in water samples with the linear sweep anodic stripping voltammetry (LSASV).The factors such as pH, deposition potential and deposition time are optimized. Under optimal conditions the wide linear concentration range from 0.05 to 40 μmol/dm3was obtained for Pb(II), with limit of detection (LOD) of 8.06 nmol/dm3 and two linear concentration ranges were obtained for Cd(II), from 0.05 to 1.6 μmol/dm3 and from 1.6 to 40 μmol/dm3, with calculated LOD of 7.02 nmol/dm3. The selectivity of the new sensor was investigated in the presence of interfering ions. The sensor is stable and it gave reproducible results. The new sensor was succesfully applied on determination of heavy metals in natural waters.

The role of humic substances in the speciation of metals in natural waters

The paper analyzes currently applied methodological approaches to evaluating the speciation of metals in natural waters and presents literature data and original author’s experimental results on the forms of metals in natural waters in various natural–climatic zones in Russia and other countries. Data are presented on the geochemical specifics of the distribution of metals between their forms in lakes RF.

Key factors in electromembrane microextraction systems for metals analysis in natural waters

ABSTRACTApplication of an electric potential to hollow fibre liquid phase microextraction (HF-LPME) systems previously optimised for metals preconcentration from natural waters could improve their analytical performance increasing enrichment factors and reducing operation times. Nevertheless, the effectiveness of the direct application of an electric potential to these systems may be limited due to the effects produced by other operational parameters.In this work, the effect of a variable electric potential on the enrichment factors of four HF-LPME systems used for the analysis of trace metals in natural waters (Cd, Ni, Ag and Cu) has been studied. In addition, the effect of organic phase composition, distance between electrodes and electrodes diameter has been also studied. From the results obtained, composition of organic phase can be considered as the key factor in electromembrane (EME) systems, since its polarity determine the operational range of the applied electric potential and consequently the enrichment factor that could be achieved.EMEs have demonstrated to be a real alternative to preconcentrate Cd, Ag and Cu from natural water samples in very short times (30 min). In fact, enrichment factors increased up to one order of magnitude if compared with HF-LPME methodology without application of an electrical potential.

Geochemical Specifics of the Distribution of Elements between Their Forms in Lakes in the European Part of Russia and Western Siberia

The paper analyzes currently applied methodological approaches to evaluating the speciation of metals in natural waters and presents literature data and original author’s experimental results on the forms of metals in natural waters in various natural–climatic zones in Russia and other countries. Data are presented on the geochemical specifics of the distribution of metals between their forms in lakes in the European part of Russia and western Siberia.

Mechanisms of Sb(III) oxidation mediated by low molecular weight phenolic acids

Quinone-like moieties are active components of natural organic matter (NOM), whose redox reactions may exert substantial influence on the behavior of trace metals in natural waters. The interactions between NOM and antimony (Sb) influence the mobility and toxicity of Sb, but the mechanism of this process is poorly understood. In this study, batch oxidation experiments were conducted to evaluate the effects of model quinone-like moieties, i.e., 1,4-hydroquinone and low molecular weight phenolic acids (LMWPAs), including gallic acid, caffeic acid, and protocatechuic acid, on the oxidation of Sb(III) in the absence of light. The results indicated that Sb(III) was rapidly oxidized to Sb(V) in the presence of different phenolic acids in neutral and alkaline conditions. The oxidative reactions were pH dependent and the Sb(III) oxidation rate constant (kobs) increased by one or two orders of magnitude when the pH shifted from 7.0 to 9.0. The combination of electron paramagnetic resonance and free radical quenching studies elucidated that reactive oxygen species (hydrogen peroxide) and quinone species (the semiquinone radical and oxidized forms of LMWPAs) were the main contributors to the Sb(III) oxidation. According to density functional theory based calculations, the bond dissociation enthalpy of the phenolic hydroxyl group is well correlated with kobs, which is in line with its pro-oxidant property towards Sb(III) through the production of semiquinone radical. The findings of this study provided new insights into the mechanism of the oxidation of Sb(III) by NOM.