Trace analysis of heavy metals in groundwater samples by ion chromatography with post-column reaction and ultraviolet-visible detection

In-fiber Mach-Zehnder interferometer based on hollow optic fiber for metal ion detection

A new, to the best of our knowledge, in-fiber Mach-Zehnder interferometric sensor is proposed and experimentally demonstrated for detecting Cu²⁺ ions in an aqueous environment. The sensor is fabricated simply and cost-effectively by arc-fusing a short section of hollow optical fiber between two standard single-mode fibers and is functionalized by depositing chitosan and poly(acrylic acid) bilayers using electrostatic self-assembly. The proposed sensor shows a linear response with sensitivity of 42 nm/mM in the Cu²⁺ ion concentration from 0 to 40 µM. Moreover, the fiber sensor exhibits good reusability and repeatability and is a promising candidate for contamination detection in drinking water and industrial waste water.

Nanostructured Shell-Layer Artificial Antibody with Fluorescence-Tagged Recognition Sites for the Trace Detection of Heavy Metal Ions by Self-Reporting Microsensor Arrays

Herein, a strategy for a metal ion-imprinted artificial antibody with recognition sites tagged by fluorescein was carried out to construct the selective sites with a sensitive optical response signal to the specific metal ion. The synthesized silica nanoparticles were modified by the derivative residue group of 3-aminopropyltriethoxysilane conjugated with a 4-chloro-7-nitro-1,2,3-benzoxadiazole (NBD-Cl) molecule through the hydrolysis and condensation reactions. The as-prepared silica nanoparticles were encapsulated by metal ion (Cu²⁺, Cd²⁺, Hg²⁺, and Pb²⁺)-imprinted polymers with nanostructured layers through the copolymerization of ethyl glycol dimethyl methacrylate (EGDMA) as a cross-linker, AIBN as an initiator, metal ions as template molecules, AA as a functional monomer, and acetonitrile as a solvent. The layers of molecular imprinted polymers (MIPs) with a core-shell structure removed template molecules by EDTA-2Na to retain the cavities and spatial sizes to match the imprinted metal ions. The microsensor arrays were achieved by the self-assembly technique of SiO₂@MIP nanoparticles on the etched silicon wafer with regular dot arrays. The nanostructured-shell layers with fluorescence-tagged recognition sites rebound metal ions by the driving force of concentration difference demonstrates the high selective recognition and sensitive detection to heavy metal ions through the decline of fluorescence intensity. The LOD concentration for four metal ions is down to 10^-9 mol·L^-1. The method will provide biomimetic synthesis, analyte screen, and detection of highly dangerous materials in the environment for theoretical foundation and technological support.

Verification of the Determination Method of Dissolved Metal Content using ICP-OES and Its Application for River Water in Bandar Lampung City

Method verification for metal analysis (Cd, Cr, Cu, Ni, Co, and Mn) in surface water using Inductively Coupled Plasma (ICP) was carried out to evaluate the method’s performance in the laboratory-based on US Method EPA 200.7. The verified method is used to determine the metal content in river water flowing in Bandar Lampung. The results showed that the method used had good linearity with a regression coefficient of more than 0.995. This method’s accuracy is expressed by the %RSD (relative standard deviation), which is in the range of 3.145 to 4.345% and meets the acceptance requirements with a %RSD value less than ⅔ CV Horwitz. The method accuracy obtained from the spiking analysis gives a range of 80-110% for the analysis of 1 mg/L and meets the acceptability required by AOAC. Overall, the performance of the method used is suitable for the analysis of metals in surface water. This method was applied for metal analysis in river water samples in several places in Bandar Lampung, which were the Palang Besi river (A1), the Way Balau Kedamaian river (B1), the Way Balau Kedaton river (C1), the Way Kuala river (D1), the Sumur Batu Kahuripan river (E1), Sumur Putri river (F1), and Muara Kahuripan river (G1). The concentrations of Cd, Cr, Cu, Ni, and Co metals were under the LoD method, while the Mn concentration was above the LoD method in river water samples.

Ion chromatography for monitoring [NTf2]- anion contaminants in pure and saline water

Hydrophobic ionic liquids containing bis(trifluoromethanesulfonyl)imide, [NTf2]-, anions partially dissolve in aqueous phases. The potential ecotoxicity of [NTf2]- means wastewater streams must be closely monitored to avoid environmental release. A new ion chromatography method is presented, which improves on existing techniques and methods by significantly decreasing analysis time and improving chromatographic peak properties. Consequently, the limit of detection is lowered to 5 μM (1.4 ppm) and limit of quantification lowered to 30 μM (8.5 ppm). The method is reproducible and has a high precision for short and medium chain length ionic liquids (RSD = 0.95%); however, microemulsion effects increase measurement errors for long chain ionic liquids (RSD = 2.32%), albeit by a relatively small amount. Hence, the method is a highly accurate analytical method for highly polarizable [NTf2]- anions, and quantification in the presence of high salinity samples, such as seawater, is readily achieved. Importantly, this method is a significant improvement on existing techniques (chromatography, NMR, UV-Vis) for many reasons, making it ideal for environmental monitoring or process design of [NTf2]- ionic liquid-based applications.

Interaction of epitaxial graphene with heavy metals: towards novel sensing platform

Development of next-generation sensors based on graphene materials, especially epitaxial graphene (EG) as the most promising representative, with desirable cross-reactivity to heavy metals (HMs) is of great technological significance in the virtue of enormous impact on environmental sensorics. Nevertheless, the mechanisms by which EG responds to toxic HMs exposure and then produces the output signal are still obscure. In the present study, the nature of interaction of toxic HMs, e.g. Cd, Hg and Pb in neutral charge state and EG on Si-face SiC in the absence and in the presence of pure water solution has been investigated using density functional theory with the inclusion of dispersion correction and cluster model of EG. The gas-phase calculations showed that adsorbed electron-donating Cd and Hg adatoms on EG are most stable when bonded to hollow sites, while Pb species prefer to sit above bridge sites. By using non-covalent interaction analysis, charge decomposition analysis, overlap population density of states analysis and topological analysis, it was found that the interaction between Cd or Hg and EG is non-bonding in nature and is mainly governed by van der Waals forces, while Pb adsorption is followed by the formation of anti-bonding orbitals in vacuum conditions and bonding orbitals in water. The role of solvent in the adsorption behavior of HMs is studied and discussed. The present theoretical analysis is in good agreement with recent experimental results towards discriminative electrochemical analysis of the toxic HMs in aqueous solutions at critically low concentrations.

Seasonal study of concentration of heavy metals in waters from lower São Francisco River basin, Brazil

In this study we determined the concentration of metals (Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn) in the water lower São Francisco River basin, to evaluate the influence of urbanization and industrialization on environmental changes in the water resource. All samples were analyzed using the IUPAC adapted method and processed in an atomic absorption spectrophotometer. The sampling stations located near the industrial areas were influenced by industrialization because they presented higher concentrations of Cd, Cr, Ni and Cu. The other sampled locations showed changes with regard the trace elements probably originating in the soil, like Fe, Zn and Pb. There was a gradual increase in the concentrations of metals, in general, in the period of highest rainfall of the hydrographic network. Overall, except for Zn and Mn, the trace elements exceeded the maximum allowed value established by national legislation (CONAMA). Lower São Francisco River basin has suffered interference from urbanization and industrialization, so awareness programs should be developed so as to control and lessen future problems.

Selective colorimetric sensing of Co2+ and Cu2+ using 1-(2-pyridylazo)-2-naphthol derivative immobilized polyvinyl alcohol microspheres

A novel optical sensor was proposed. The sensor can be used to monitor Co²⁺ and Cu²⁺ ions.

Detection of heavy metals in water using dye nano-complexants and a polymeric film

An optical analytical method, based on complexation reactions of organic azo-dyes with heavy metals, is proposed. It is based on a specially designed polymeric film that when submerged in water contaminated with heavy metals it changes its color. The azo-dyes are injected into the tested water, resulting in formation of nano-particles of insoluble complexes. The polymeric film embeds and dissolves these nano-particles and thus allows for spectral and/or visual analysis. This film consists of a PVC polymeric skeleton and an organic solvent, bis(2-ethylhexyl)phthalate, which possesses high affinity to the heavy metal nano-complexes. The method was exemplified for Cd, Ni and Co ions. The method is sensitive in the sub-ppm range. The mechanism and kinetics of the film coloration were reported.

Fast simultaneous determination of traces of Cu(II) and Co(II) in soils and sediments with the luminol/perborate chemiluminescent system

A flow injection analysis method based on ion chromatography and luminol chemiluminescence detection was used for the simultaneous determination of copper (II) and cobalt (II) trace levels in soils and sediments following microwave-assisted acid digestion. Detection was based on chemiluminescence (CL) of the luminol-perborate system in an alkaline medium, which is catalyzed by both transition metals. The concentration and pH of the eluent (oxalic acid) was found to affect CL intensities and retention times, both of which were inversely proportional to the oxalic acid concentration. The calibration curves for both metal ions were linear and allowed a limit of detection of 0.003 μg l(-1) for cobalt (II) and 0.014 μg l(-1) for cooper (II) to be calculated. The proposed method was successfully used to determine both metal ions in certified reference materials of stream and river sediments and soil samples. Based on the results, the determination is free of interferences from the usual concomitant ions.

Determination of trace transition metals in environmental matrices by chelation ion chromatography

Trace transition metals (Fe(3+), Mn, Cu, Cd, Co, Zn, Ni) in environmental samples were analyzed by chelation ion chromatography using a mixed bed ion-exchange column with pyridine-2,6-dicarboxylic acid (PDCA) and oxalic acid as eluent and large volume direct injection (1,000 μl). The two eluents, PDCA and oxalic acid, were tested, and repeatability and detection limits were compared. The total analysis time was ~15 min. The separation with PDCA was more successful than that obtained with acid oxalic. It was observed that utilizing PDCA resulted in lower detection limits, higher repeatability, and a quantitative detection of Cd and Mn, which coelute as a single peak when using the oxalic acid. At last, the PDCA calibration graphs resulted linear (r (2) > 0.999) in the range 0.4-1,000 μg/L. The procedure was applied to the analysis of metals in soils and in water samples. The results obtained from the analysis of natural waters have demonstrated that the method is simple and efficient, therefore, can be used for the determination of metals in natural waters using a continuous and automatic monitoring system.

Valores de background geoquímico e suas implicações em estudos ambientais

O estabelecimento de valores de background geoquímico como medida relativa para distinguir concentrações naturais de um elemento (geogênica e/ou biogênica) e a influência das atividades antrópicas nestas concentrações representa um dos assuntos mais importantes das ciências ambientais recentes. A relação entre as alterações naturais e as proporcionadas pela ação antrópica nas espécies químicas é uma questão que envolve implicações importantes nas áreas da geologia, toxicologia e biologia, entre outros campos do conhecimento. Isto é especialmente importante, quando interpretações geoquímicas de elementos tóxicos são requeridas. Assim, o objetivo principal desse artigo é apresentar e discutir as razões pelas quais o estabelecimento de valores de background geoquímico tem implicações nos estudos ambientais. Ao longo desse artigo, são apresentados alguns conceitos de background geoquímico e os principais métodos utilizados para avaliar a concentração background de elementos químicos (métodos direto e indireto). Além disso, são destacados alguns exemplos de estudos desenvolvidos no Brasil. Estudos envolvendo o estabelecimento de valores de background geoquímico são importantes porque permitem avaliar riscos potenciais de contaminação e identificar concentrações naturais de elementos-traço de uma determinada área.

Simultaneous Spectrophotometric Determination of Cobalt and Nickel by Partial Least Square Regression in Micellar Media

Diphenycarbazone has been used for the simultaneous determination of cobalt and nickel by partial least square regression method. DPC complexes of cobalt and nickel at pH 7-10 are of pink color, which are soluble in TX-100 micellar media. A partial least square multivariate calibration method for the analysis of binary mixtures of cobalt and nickel was developed. The total relative standard error for applying the PLS method was calculated. The accuracy and reproducibility of the determination method for various known amounts of Co(II) and Ni(II) in their binary mixtures were tested. The effects of diverse ions on the determination of cobalt and nickel to investigate the selectivity of the method were also studied. The proposed method was applied to the synthetic binary mixtures, alloys and pharmaceutical samples.

Chromatographic separation of certain metal ions using a bifunctional quaternary ammonium-sulfonate mixed bed ion-exchanger

The separation behaviour of Pb(2+), Cu(2+), Cd(2+), Co(2+), Zn(2+) and Ni(2+) on bifunctional quaternary ammonium-sulfonate mixed ion-exchangers (Dionex, IonPac CS5 and CG5) was studied using different eluents including solutions of oxalic acid, potassium oxalate, sodium oxalate and ammonium oxalate. Separated metal ions were followed by using 4-(2-pyridylazo) resorcinol (PAR) as post-colouring complex. The retention factors of different ions proved to be dependent on the pH, concentration, nature of each complexing agent, and to less extent on eluent flow rate. The retention behaviour and separation mechanism of complexed metal analytes are discussed in the light of the stability of metal complexes and the ligand complexing ability of used eluent. Comparison between various mobile phases is evaluated, and both sodium and potassium oxalate can be used successfully for simultaneous separation of studied metals with good resolution within short elution periods. The method can be used in different applications including analysis of bottled water from different resources.

The determination of trace metal pollutants in environmental matrices using ion chromatography

A review is presented detailing the development of ion chromatography (IC) as a selective analytical tool for the determination of toxic metals and their organic species in many environmental sample matrices. A brief outline of ion chromatographic principles, together with an overview of the stationary phases used to separate metals, namely ion exchangers, modified ion pair sorbents and chelating ion exchangers, and the methods for detecting metal ions including hyphenation with spectroscopy and sample preparation schemes are also given, prior to a critical examination of developed methods for various metals including arsenic, chromium, cadmium, lead, mercury, beryllium, aluminium and uranium since 1990.

Sample enrichment by using monolithic precolumns in microcolumn liquid chromatography

An on-line sample enrichment system was designed using monolithic precolumns in microcolumn LC. The monolithic ODS capillary columns were prepared via in situ sol-gel processes. The enrichment efficiency of the monolithic columns was tested by using phthalates as the analytes. The relative standard deviations (n = 6) for the retention time, peak area and peak height were between 0.4 and 1.2%, 0.9 and 5.5% and 0.4 and 3.9%, respectively. The system was linear (R2 > 0.99) within the working sample concentration and sample volume ranges. Comparing to 0.2 microl injection with a typical sample injector, the theoretical plate number of a same separation column was increased by 3-6-fold when the precolumn unit was used for sample injection. The recoveries of the analytes were between 88 and 120%, and the sample volume that could be injected into the system was increased up to 5000-fold. The limits of detection were improved by more than 2000-fold and were between 0.21 and 0.87 ng ml(-1) even with a UV absorbance detector. This system was applied to the determination of phthalates contained in laboratory distilled water and tap water samples.

The importance of capillary electrophoresis, capillary electrochromatography, and ion chromatography in separations of inorganic ions

The importance of capillary electrophoresis (CE), capillary electrochromatography (CEC), and ion chromatography (IC) in inorganic ion analyses is outlined. Methods for improving the reliability of the CE measurements are briefly described. Selectivity optimization in CE analyses of inorganic cations and anions is discussed. Using the Peakmaster program, CE system peaks (system zones, eigenmobilites) and some important CE parameters, such as effective mobilities, electromigration dispersion, indirect UV, and direct conductivity signals, are predicted and compared with experimental analyses.

Determination of lanthanides in synthetic standards by reversed-phase high-performance liquid chromatography with the aid of a weighted least-squares regression model estimation of method sensitivities and detection limits

A reversed-phase liquid chromatography method was used for determining lanthanides in synthetic standards. The separation of lanthanide group was achieved in less than 15 min using a linear gradient program of alpha-hydroxyisobutyricacid eluent from 0.05 to 0.5 M (pH 3.8) with a UV-Vis detection system at 658 nm. A post-column reagent of Arsenazo III was employed for improving the sensitivity and selectivity of the method as well as for lowering the limits of detection (LODs). Linear calibration curves for all lanthanides were constructed using an ordinary least-squares (OLS) regression as well as a weighted least-squares (WLS) regression model for taking into account the heteroscedastic errors. The WLS model was successfully used for a better estimation of the sensitivities and the LODs of the RP-HPLC method than the conventional OLS model. The lanthanide sensitivity obtained from the slope of each calibration curve seems to be better for a lanthanide with an odd-atomic number compared to its neighboring element with an even-atomic number, as if nature is helping us to quantify the concentrations of the less abundant lanthanides. This observation was also confirmed when the LODs computed for all lanthanides were examined. The LODs observed for all lanthanides depicted a clear systematic "zigzag" pattern. This is actually the first time that the lanthanide detection limits determined by a HPLC method are shown to mimic the zigzag patterns for the concentration data in geological and cosmological materials. Such a "zigzag" pattern should be used as a standard criterion for evaluating the quality of detection limit data.