Cloud point extraction for high-performance liquid chromatographic speciation of Cr(III) and Cr(VI) in aqueous solutions

Cloud point extraction (CPE) was applied as a preconcentration step for HPLC speciation of chromium in aqueous solutions. Simultaneous preconcentration of Cr(III) and Cr(VI) in aqueous solutions was achieved by CPE with diethyldithiocarbamate (DDTC) as the chelating agent and Triton X-114 as the extractant. Baseline separation of the DDTC chelates of Cr(III) and Cr(VI) was realized on a RP-C18 column with the use of a mixture of methanol-water-acetonitrile (65:21:14, v/v) buffered with 0.05 M NaAc-HAc solution (pH 3.6) as the mobile phase at a flow rate of 1.0 ml min(-1). The precision (R.S.D.) for eight replicate injections of a mixture of 100 microg l(-1) of Cr(III) and Cr(VI) were 0.6 and 0.5% for the retention time, 4.1 and 4.6% for the peak area measurement, respectively. The concentration factor, which is defined as the concentration ratio of the analyte in the final diluted surfactant-rich extract ready for HPLC separation and in the initial solution, was 65 for Cr(III) and 19 for Cr(VI). The linear concentration range was from 50 to 1000 microg l(-1) for Cr(III) and 50-2000 microg l(-1) for Cr(VI). The detection limits of Cr(III) and Cr(VI) were 3.4 and 5.2 microg l(-1), respectively. The developed method was applied to the speciation of Cr(III) and Cr(VI) in snow water, river water, seawater and wastewater samples.     

Selective and efficient uphill transport of Cu(II) through liquid membrane

1,2-Bis methyl (2-aminocyclopentene carbodithioate) ethane is an excellent synthetic carrier for efficient and specific transport of Cu(II) ions through a liquid membrane and has the ability to transport Cu(II) ions uphill.     

Solid-phase extraction-liquid chromatography-fluorimetry for organotin speciation in natural waters

Summary A method is reported for the determination of dibutyltin (DBT), diphenyltin (DPhT), tributyltin (TBT), and triphenyltin (TPhT) species at the nanogram per litre concentration level in natural water samples. Analytes were isolated from samples by solid-phase extraction and analysed both off-line and on-line by reversed-phase high-performance liquid chromatography with post-column derivatization and fluorimetric detection. Several SPE cartridges and eluents were evaluated; C₁₈ enrichment and elution with a mixture of methanol, acetic acid, and water was found most suitable. Preconcentration factors up to 250 can be achieved when a 500-mL sample is processed. Detection limits, recovery rates, and the precision of the whole process have been determined. The method has been applied to the determination of organotin species in spiked natural water samples collected on the NW Mediterranean coast. Recovery rates range from 75 to 110% and detection limits are at the low ng L⁻¹ level (1–3 ng Sn L⁻¹ for DPhT, DBT, and PhT and 40 ng Sn L⁻¹ for TBT when 250 mL spiked sea water is processed.)     

Co(II) and Cu(II) complexes of 2,4-diamino-5-(3,4,5-trimethoxybenzyl)pyrimidine

The Co(II) and Cu(II) complexes of 2,4-diamino-5-(3,4,5-trimethoxybenzyl)pyrimidine (trimethoprim) were synthesized and characterized by elemental analysis, UV-Vis and IR spectroscopy, magnetic susceptibility measurements, EPR (Cu complexes) and single crystal X-ray studies. The molecular structures of the compounds consist of dimeric metal ions in distorted octahedral environments, bridged with four acetate ions and each metal ion coordinated to one trimethoprim through the pyrimidinyl nitrogen atom.     

Voltammetric methods for speciation analysis of trace metals in natural waters

Trace metals play an important role in the regulation of primary productivity and phytoplankton community composition. Metal species directly affects the biogeochemical cycling processes, transport, fate, bioavailability and toxicity of trace metals. Therefore, developing powerful methods for metal speciation analysis is very useful for research in a range of fields, including chemical and environmental analysis. Voltammetric methods, such as anodic stripping voltammetry (ASV) and competing ligand exchange-adsorptive cathodic stripping voltammetry (CLE-AdCSV), have been widely adopted for speciation analysis of metals in different natural aquatic systems. This paper provides an overview of the theory of voltammetric methods and their application for metal speciation analysis in natural waters, with a particular focus on current voltammetric methods for the discrimination of labile/inert fractions, redox species and covalently bound species. Speciation analysis of typical trace metals in natural waters including Fe, Cu, Zn, Cd, and Pb are presented and discussed in detail, with future perspectives for metal speciation analysis using voltammetric methods also discussed. This review can elaborate the particular knowledge of theory, merits, application and future challenge of voltammetric methods for speciation analysis of trace metals in natural waters.     

Investigation of the interaction of olefin-bonded transition metal complexes by gas chromatography. II. Phosphine complexes of Cu(II)

Summary Packings consisting of chemically bonded diphenylphosphine complexes with CuCl₂ and CuBr₂ were synthesized and their retention parameters determined. The packings investigated are capable of specific interactions with electron-donating compounds and are characterized by particularly high selectivity in relation to cis and trans isomers allowing their complete separation.Part 1: see ref. [1]     

Stripping voltammetry for the determination of trace metal speciation and in-situ measurements of trace metal distributions in marine waters

Progress in marine chemistry has been driven by improved sampling and sample handling techniques, and developments in analytical chemistry. Consequently, during the last 20 years our understanding of marine trace metal biogeochemistry has improved a great deal. Stripping voltammetric techniques (anodic stripping voltammetry and adsorptive cathodic stripping voltammetry) have made an important contribution to this understanding. The selectivity and extremely low detection limits have made stripping voltammetry a widely used technique for trace metal speciation and trace metal distribution measurements in seawater. Stripping voltammetry is very suitable for ship-board and in-situ applications because of the portability, low cost and capability for automation of the voltammetric instrumentation. Future developments in stripping voltammetry can be expected in the field of stand-alone submersible voltammetric analysers, capable of continuous trace metal measurements. Future applications of stripping voltammetry can be found in the interactions between trace metal speciation and growth and the functioning of organisms in pristine and metal polluted marine waters.     

Separtation of metal tetrakis(p-tolyl)porphine complexes by reversed-phase high-performance liquid chromatography

Summary The feasibility of reversed-phase high-performance liquid chromatography for the separation of several metal complexes ofmeso-tetrakis(p-tolyl)porphine (TTP) is described. A combination of an octadecyl-bonded stationary phase with a non-aqueous polar mobile phase, such as an acetone-acetonitrile mixture, has proved effective for the separation. Thus, the TTP complexes of Mg, VO, Ni, Cu, Zn, and Pd and also TTP free acid were successfully separated in about 10min on a Li-Chrosorb RP-18 column (7m, 250×4mm i.d.) with a 7030 (vol/vol) mixture of acetone and acetonitrile at a flow-rate of 1 mlmin^–1.     

Determination of free copper concentrations in natural waters by using supported liquid membrane extraction under equilibrium conditions

A method is described for measurement of freely dissolved copper concentrations in natural water samples using supported liquid membrane (SLM) extraction under equilibrium conditions, a technique denoted equilibrium sampling through membranes (ESTM). For this purpose, 1,10-dibenzyl-1,10-diaza-18-crown-6 as neutral carrier and oleic acid were used in the membrane phase. The main variables optimised were the carrier used to form the metal complexes, the organic solvent used in the membrane, the countercation, pH, the ligand used in the acceptor phase, the extraction time, and the flow rate of the donor phase. After the optimisation process an enrichment factor of 18.5 was obtained. Equilibrium conditions were reached after extraction for 60 min if a flow rate of 1.0 mL min^–1 or greater was used. When different ligands such as humic acids, phthalic acid, and EDTA were added to the sample solution, and sample pH ranged from 6 to 8, the results obtained for freely dissolved copper concentrations were in a good agreement with results from speciation calculations performed with Visual Minteq V 2.30, Cheaqs V L20.1, and WinHumic V. The developed technique was applied to analysis of stream and leachate water.Electronic Supplementary Material Supplementary material is available for this article at     

Voltammetric determination of Cu(II) in natural waters and human hair at a meso-2,3-dimercaptosuccinic acid self-assembled gold electrode

An electrochemical sensor for the detection of copper(II) ions is described using a meso-2,3-dimercaptosuccinic acid (DMSA) self-assembled gold electrode. First in ammonia buffer pH 8, copper(II) ions complex with self-assembled monolayer (SAM) via the free carboxyl groups on immobilized meso-2,3-dimercaptosuccinic acid (accumulation step). Then, the medium is exchanged to acetate buffer pH 4.6 and the complexed Cu(II) ions are reduced in negative potential of −0.3 V (reduction step). Following this, reduced coppers are oxidized and detected by differential pulse (DP) voltammetric scans from −0.3 to +0.7 V (stripping step). The effective parameters in sensor response were examined. The detection limit of copper(II) was 1.29 μg L⁻¹ and R.S.D. for 200 μg L⁻¹ was 1.06%. The calibration curve was linear for 3-225 μg L⁻¹ copper(II). The procedure was applied for determination of Cu(II) to natural waters and human hairs. The accuracy and precision of results were comparable to those obtained by flame atomic absorption spectroscopy (FAAS).     

Application of dispersive liquid-liquid microextraction combined with high-performance liquid chromatography for the determination of methomyl in natural waters

A new method was developed for determination of methomyl in water samples by combining a dispersive liquid-liquid microextraction (DLLME) technique with HPLC-variable wavelength detection (VWD). In this extraction method, 0.50 mL of methanol (as dispersive solvent) containing 20.0 microL of tetrachloroethane (as extraction solvent) was rapidly injected by syringe into a 5.00-mL water sample containing the analyte, thereby forming a cloudy solution. After phase separation by centrifugation for 2 min at 4000 rpm, the enriched analyte in the settled phase (8 +/- 0.2 microL) was at the bottom of the conical test tube. A 5.0-microL volume of the settled phase was analyzed by HPLC-VWD. Parameters such as the nature and volume of the extraction solvent and the dispersive solvent, extraction time, and the salt concentration were optimized. Under the optimum conditions, the enrichment factor could reach 70.7 for a 5.00-mL water sample and the linear range, detection limit (S/N = 3), and precision (RSD, n = 6) were 3-5000 ng/mL, 1.0 ng/mL, and 2.6%, respectively. River and lake water samples were successfully analyzed by the proposed method. Comparison of this method with solid-phase extraction, solid-phase microextraction, and single-drop microextraction, indicates that DLLME combined with HPLC-VWD is a simple, fast, and low-cost method for the determination of methomyl, and thus has tremendous potential in trace analysis of methomyl in natural waters.     

Capillary electrophoretic speciation of Cu(II) and Co(III) in the electroless copper plating baths

Summary A capillary electrophoretic method for the determination of Cu(II) and Co(III) chelates with ethylenediamine in electroless copper plating baths has been developed. The influence of carrier electrolyte parameters such as nature of counter-ion and pH were studied and discussed. The optimised separations were carried out in a fused silica capillary (57 cm × 75 μm I.D.) filled with an ethylenediamine sulfate electrolyte (20 mol L⁻¹ ethylendiamine, pH7.0 with H₂SO₄; applied voltage, +25 kV) using direct UV detection at 214 nm. The detection limits for a signalto-noise ratio of 3 and 10s hydrodynamic injection were 5×10⁻⁶ mol L⁻¹ for Cu(II) and 1×10⁻⁶ mol L⁻¹ for Co(III). The relative standard deviations of the peak areas for Cu(II) and Co(III) were found to be 1.5% and 2.4%, respectively, with five consecutive injections of standard solution containing 5×10⁻⁵ mol L⁻¹ of each metal ion. Application of the method to the speciation of Cu(II) and Co(III) complexes in copper plating bath samples is also demonstrated.     

Application of multivariate self-modeling curve resolution to the quantitation of trace levels of organophosphorus pesticides in natural waters from interlaboratory studies

Multivariate self-modeling curve resolution is applied to the quantitation of coeluted organophosphorus pesticides: fenitrothion, azinphos-ethyl, diazinon, fenthion and parathion-ethyl. Analysis of these pesticides at levels of 0.1 to 1 μg/l in the presence of natural interferences is achieved using automated on-line liquid-solid extraction (Prospekt) coupled to liquid chromatography and diode array detection followed by a recently developed multivariate self-modeling curve resolution method. The proposed approach uses only 100 ml of natural water sample and has improved resolution of the coeluted organophosphorus insecticides and their quantitation at trace level. The results have been compared with those obtained by different laboratories participating in the Aquacheck interlaboratory exercise (WRC, Medmenham, UK) where more conventional analytical techniques are being used.     

Spectrophotometric determination of Cu(II) with sequential injection analysis

A sequential injection system, based on the reaction of Cu(II) with diethyldithiocarbamate (DDTC), was developed for the determination of Cu(II) in plant food and water samples. The extraction procedure, generally used to extract the Cu(II)–DDTC complex for subsequent analysis was eliminated in this procedure. The complex was detected spectrophotometrically in aqueous solutions at 460 nm. The physical and chemical parameters depicting the system were studied to obtain optimum conditions for sample analysis. The system developed is fully computerized and able to monitor Cu(II) in samples at seven samples per hour with a relative standard deviation of <4.50%. The calibration curve is linear from 0.5–5.0 mg/l with a detection limit of 0.2 mg/l. Interferences were reduced by introducing multiple flow reversals, to increase mixing between the reagent and sample zones, and subsequently enhance working of the masking agents (EDTA/citrate).     

Speciation of Cu(II) with a flow-through permeation liquid membrane: discrimination between free copper, labile and inert Cu(II) complexes, under natural water conditions

Metal toxicity is not related to the total metal ion concentration, but to those of some specific Cu(II) species. The Permeation Liquid Membrane technique is based on the carrier-mediated transport of the test metal across a hydrophobic membrane and enables discrimination between various trace metal species in solution. The present work shows how the labile and inert Cu(II) complexes can be determined selectively, by varying the flow-rate of the test solution, in a flow-through cell. A mathematical model of metal flux through the PLM, based on diffusion-limited transport under steady-state conditions, is described. The model and the performance of the technique were studied in well-defined synthetic solutions containing simple organic hydrophilic ligands forming either inert (nitrilotriacetic acid), or labile complexes with Cu(II) (tartaric acid, malonic acid). The results were compared with theoretical predictions of thermodynamic species distribution in solution. Uncertainties on stability constants for copper speciation calculation were taken into account. The detection limits of the device are discussed. This work demonstrates that the flow-through cell is a reliable tool for copper speciation measurements in natural waters.     

Substitution behavior of square-planar and square-pyramidal Cu(II) complexes with bio-relevant nucleophiles

Substitution reactions of [CuCl₂(en)] and [CuCl₂(terpy)] complexes (where en = 1,2-diaminoethane and terpy = 2,2′:6′,2″-terpyridine) with bio-relevant nucleophiles such as inosine-5′-monophosphate (5′-IMP), guanosine-5′-monophosphate (5′-GMP), L-methionine (L-Met), glutathione (GSH) and DL-aspartic acid (DL-Asp) have been investigated at pH 7.4 in the presence of 0.010 M NaCl. Mechanism of substitution was probed via mole-ratio, kinetic, mass spectroscopic and EPR studies at pH 7.4. In the presence of an excess of chloride, the octahedral complex anion [CuCl₄(en)]^2? is formed rapidly while equilibrium reaction was observed for [CuCl₂(terpy)]. Different order of reactivity of bio-molecules toward Cu(II) complexes was observed. Mass spectrum of [CuCl₂(terpy)] in Hepes buffer has shown two new signals at m/z = 477.150 and m/z = 521.00, assigned to [CuCl(terpy)]⁺-Hepes fragments of coordinated Hepes buffer. These signals also appear in the mass spectra of ligand substitution reactions between [CuCl₂(terpy)] and bio-molecules in molar ratio 1:1 and 1:2. According to EPR data, L-Met forms the most stable complex with [CuCl₂(en)] among the ligands considered, while [CuCl₂(terpy)] complex did not show significant changes in its square-pyramidal geometry in the presence of the buffer or bio-ligands.     

Structural and biological behaviors of some nonionic Schiff-base amphiphiles and their Cu(II) and Fe(III) metal complexes

Novel series of nonionic Schiff bases was synthesized and characterized using microelemental analysis, FTIR and (1)H NMR spectra. These Schiff bases and their complexes with Cu and Fe have been evaluated for their antibacterial activity against bacterial species such as Staphylococcus aureus, Pseudomonas aureus, Candida albi, Bacillus subtilis and Escherichia coli and their fungicidal activity against Aspcrgillus niger and Aspcrgillus flavus. The results of the biocidal activities showed high potent action of the synthesized Schiff bases towards both bacteria and fungi. Furthermore, complexation of these Schiff bases by Cu(II) and Fe(III) show the metal complexes to be more antibacterial and antifungal than the Schiff bases. The results were correlated to the surface activity and the transition metal type. The mode of action of these complexes was discussed.     

Response of the jalpaite membrane copper(II) ion-selective electrode in marine waters

The response of the Orion 94-29 Cu^II ion-selective electrode (ISE) [employing a jalpaite membrane] in seawater has been related to levels of free Cu^II yielding results for the Derwent River and San Diego Bay that are 2 to 3 orders of magnitude higher than those for the Pacific Ocean. Response data for the electrode in acidified seawater at pH 2 are internally consistent with total Cu^II levels determined using differential pulse anodic stripping voltammetry (DPASV) and graphite furnace atomic absorption spectrometry (GFAAS). It has been found that, even in acidified seawater, the organic ligands influence the response of the electrode, and this effect can be compensated successfully by either analyzing UV-photooxidized seawater and/or using a standard addition technique. The assigned ISE results for total Cu^II in acidified seawater fall within ± (0.1–0.5) pCu unit of values determined using GFAAS. Electrode drift in seawater can be minimized by using a polished electrode that has been conditioned in seawater for 24 h. The improved response rate of a conditioned ISE minimizes electrode soaking times and sample contamination through membrane corrosion.     

Instability mechanisms of supported liquid membranes for copper (II) ion extraction

The instability of supported liquid membranes (SLMs) for use in copper (II) ion extraction was investigated in this paper. The degradation behavior of these SLMs was monitored in situ by electrochemical impedance spectroscopy (EIS). The electrical properties of a SLM cell can be described by an equivalent circuit, R_s(C_mR_m)Q. The model parameters, membrane resistance (R_m) and membrane capacitance (C_m) can be used to characterize the degradation behavior of SLMs. Experimental data for R_m and C_m indicated that the loss of membrane liquid (ML) during the mass transfer process consists of three stages. Results also suggest that emulsion formation was the dominant instability mechanism for these SLMs. The solubility and osmotic pressure were also shown to not be major factors contributing to the instability although both contributed to the loss of the liquid membrane. The pore size of the polymeric support increased during the first run but remained almost constant in subsequent runs.     

Automated dynamic liquid-liquid-liquid microextraction followed by high-performance liquid chromatography-ultraviolet detection for the determination of phenoxy acid herbicides in environmental waters

Automated dynamic liquid-liquid-liquid microextraction (D-LLLME) controlled by a programmable syringe pump and combined with HPLC-UV was investigated for the extraction and determination of 5 phenoxy acid herbicides in aqueous samples. In the extraction procedure, the acceptor phase was repeatedly withdrawn into and discharged from the hollow fiber by the syringe pump. The repetitive movement of acceptor phase into and out of the hollow fiber channel facilitated the transfer of analytes into donor phase, from the organic phase held in the pore of the fiber. Parameters such as the organic solvent, concentrations of the donor and acceptor phases, plunger movement pattern, speed of agitation and ionic strength of donor phase were evaluated. Good linearity of analytes was achieved in the range of 0.5-500 ng/ml with coefficients of determination, r2 > 0.9994. Good repeatabilities of extraction performance were obtained with relative standard deviations lower than 7.5%. The method provided up-to 490-fold enrichment within 13 min. In addition, the limits of detection (LODs) ranged from 0.1 to 0.4 ng/mL (S/N = 3). D-LLLME was successfully applied for the analysis of phenoxy acid herbicides from real environmental water samples.