Theoretical and analytical characterization of a flow-through permeation liquid membrane with controlled flux for metal speciation measurements

Speciation measurements with the permeation liquid membrane (PLM) technology require necessarily a good control of the flux of the analyte. In this perspective, a PLM-based multichannel flow-through cell has been designed. The first objective of this study has been to adapt the classical Levich model commonly used for electrochemical flow devices to the characteristic geometry of the PLM cell. In the latter case and contrary to the Levich model, the effects of the channel lateral walls on the flux of active species through the membrane have to be taken into account. The problem was solved by considering the existence of two parabolic Poiseuille profiles perpendicular to each other and developing along the fluid motion. The theoretical results obtained match satisfactorily with experimental data. The analytical study of this PLM system has been performed with copper(II) ions as test species and has shown that the preconcentration factor is (1) linear at least for preconcentration times of < or = 120 min, (2) reproducible on the same membrane as well as on different membranes, and (3) independent of the initial test metal ion concentration in the sample solution. The capabilities of this cell to determine metal speciation by considering lability of complexes and the flux of metal at variable flow rates of the test solution is also discussed by means of Cu(II)/sulfosalicylic complexes.     

Roles of metal ion complexation and membrane permeability in the metal flux through lipophilic membranes. Labile complexes at permeation liquid membranes

The various physicochemical factors that influence the flux of carrier-transported metal ions through permeation liquid membranes (PLM) are studied systematically. Understanding PLM behavior is important (i) to optimize the application of PLM as metal speciation sensors in environmental media and (ii) because PLM may serve as bioanalogical devices that help to elucidate the environmental physicochemical processes occurring at the surface of biological membranes. Diffusion of free and complexed metal ions in solution, as well as diffusion of the metal carrier complex in the membrane, is considered. The respective roles of diffusion layer thickness, ligand concentration, complex stability, carrier concentration, and membrane thickness are studied experimentally in detail and compared with theory, using various labile complexes, namely, Pb(II)-diglycolate, Cu(II)-diglycolate, and Cu(II)-N-(2-carboxyphenyl)glycine. Conditions where either membrane diffusion or solution diffusion is rate limiting are clearly discriminated. It is shown in particular, that, by tuning the carrier concentration or membrane thickness, either the free metal ion concentration or the total labile metal species are measured. PLM can thus be used to determine whether models based on the free ion activity in solution (such as BLM or FIAM models) are applicable to metal uptake by microorganisms in a real natural medium.     

Permeation liquid membrane metal transport: studies of complex stoichiometries and reactions in Cu(II) extraction with the mixture 22DD-laurate in toluene/phenylhexane

The role of lauric acid (LAH) in the transport of copper(II) through a permeation liquid membrane (PLM) comprising 1,10-didecyldiaza-18-crown-6 (22DD) and lauric acid (ratio 1:1) in 1:1 v/v toluene/phenylhexane has been investigated by determining the stoichiometry of metal extraction and of the metal complex formed in the organic phase by performing 1H NMR and liquid/liquid and liquid/membrane extraction measurements. In the absence of copper(II), the 1H NMR data suggest that there is a strong interaction between the proton of LAH and the nitrogen of the 22DD macrocycle but no interaction between the aliphatic long chains of LAH and 22DD. Thus, in the organic solution, the two compounds are associated as (22DD-H)(+)-LA-, the laurate being away from (22DD-H)+. The signal intensity of the acidic proton was found to decrease when the metal Pb(II) was incorporated by the carrier after its extraction from the aqueous phase. Additionally, liquid/liquid as well as liquid/membrane extraction results reveal that Cu(II) extraction proceeds via the loss of two protons from the organic phase. The Cu(II) is found to be located in the 22DD cavity and the stoichiometry of the complex in the organic phase is (22DD-Cu)(2+)-2LA-. Metal extraction is governed by 22DD and laurate acts only as counteranion. An unexpected feature was observed in the liquid/liquid extraction which was that, at low 22DD and LAH concentrations, the slope for log(Kp) = f(pH) was 2 whereas it was much lower at high carrier concentration. This unexpected result seems to stem from impurities present in 22DD: only 0.1 mol% of impurity can indeed influence the exchange ratio of Cu(II) and H+. This type of anomaly, however, is not found in the normal procedure of liquid/membrane extraction possibly due to the lower carrier/metal molar ratio which is used in the classical PLM conditions.     

Chemically modified activated carbon with 1-acylthiosemicarbazide for selective solid-phase extraction and preconcentration of trace Cu(II), Hg(II) and Pb(II) from water samples

A new sorbent 1-acylthiosemicarbazide-modified activated carbon (AC-ATSC) was prepared as a solid-phase extractant and applied for removing of trace Cu(II), Hg(II) and Pb(II) prior to their determination by inductively coupled plasma optical emission spectrometry (ICP-OES). The separation/preconcentration conditions of analytes were investigated, including effects of pH, the shaking time, the sample flow rate and volume, the elution condition and the interfering ions. At pH 3, the maximum static adsorption capacity of Cu(II), Hg(II) and Pb(II) onto the AC-ATSC were 78.20, 67.80 and 48.56 mg g⁻¹, respectively. The adsorbed metal ions were quantitatively eluted by 3.0 mL of 2% CS(NH₂)₂ and 2.0 mol L⁻¹ HCl solution. Common coexisting ions did not interfere with the separation. According to the definition of IUPAC, the detection limits (3σ) of this method for Cu(II), Hg(II) and Pb(II) were 0.20, 0.12 and 0.45 ng mL⁻¹, respectively. The relative standard deviation under optimum conditions is less than 4.0% (n = 8). The prepared sorbent was applied for the preconcentration of trace Cu(II), Hg(II) and Pb(II) in certified and water samples with satisfactory results.     

Solid-phase extraction of Mn(II), Co(II), Ni(II), Cu(II), Cd(II) and Pb(II) ions from environmental samples by flame atomic absorption spectrometry (FAAS)

A new method using a column packed with Amberlite XAD-2010 resin as a solid-phase extractant has been developed for the multi-element preconcentration of Mn(II), Co(II), Ni(II), Cu(II), Cd(II), and Pb(II) ions based on their complex formation with the sodium diethyldithiocarbamate (Na-DDTC) prior to flame atomic absorption spectrometric (FAAS) determinations. Metal complexes sorbed on the resin were eluted by 1 mol L(-1) HNO3 in acetone. Effects of the analytical conditions over the preconcentration yields of the metal ions, such as pH, quantity of Na-DDTC, eluent type, sample volume and flow rate, foreign ions etc. have been investigated. The limits of detection (LOD) of the analytes were found in the range 0.08-0.26 microg L(-1). The method was validated by analyzing three certified reference materials. The method has been applied for the determination of trace elements in some environmental samples.     

Silicon nanowires-based fluorescence sensor for Cu(II)

Si nanowires (SiNWs) were covalently modified by fluorescence ligand, N-(quinoline-8-yl)-2-(3-triethoxysilyl-propylamino)-acetamide (QlOEt) and finally formed an optical sensor to realize a highly sensitive and selective detection for Cu(II). The QlOEt-modified SiNWs sensor has sensitivity for Cu(II) down to 10(-8) M, which is more sensitive than QlOEt alone. Metal ions interferences have no observable effect on the sensitivity and selectivity of QlOEt-modified SiNWs sensor. The SiNWs-based fluorescence sensor is reversible by addition of acid to replace Cu(II). The sensing mechanisms of QlOEt-modified SiNWs to Cu(II) and the rationale for the increase in sensitivity and selectivity of QlOEt-modified SiNWs over QlOEt on Cu(II) are discussed. The current sensor structure may be extendable to other chemo- and biosensors, and even to nanosensors for direct detection of specific materials in intracellular environment.     

Effect of Zn addition on non-resonant third-order optical nonlinearity of the Cu-doped germano-silicate optical glass fiber

Cu/Zn-codoped germano-silicate optical glass fiber was manufactured by using the modified chemical vapor deposition (MCVD) process and solution doping process. To investigate the reduction effect of Zn addition on Cu metal formation in the core of the Cu/Zn-codoped germano-silicate optical glass fiber, the optical absorption property and the non-resonant third-order optical nonlinearity were measured. Absorption peaks at 435 nm and 469 nm in the Cu/Zn-codoped germano-silicate optical glass fiber were contributed to Cu metal particles and ZnO semiconductor particles, respectively. The effective non-resonant optical nonlinearity, gamma, of the Cu/Zn-codoped germano-silicate optical glass fiber was measured to be 1.5097 W(-1) x km(-1) by using the continuous-wave self-phase modulation method. The gamma of the Cu/Zn-codoped germano-silicate optical glass fiber was about four times larger than that of the reference germano-silicate optical glass fiber without any dopants. The increase of the effective non-resonant optical nonlinearity, gamma, of the Cu/Zn-codoped germano-silicate optical glass fiber, can be attributed to the enhanced nonlinear polarization due to incorporated ZnO semiconductor particles and Cu metal ions in the glass network. The Cu/Zn-codoped germano-silicate optical glass fiber showed high nonlinearity and low transmission loss at the optical communication wavelength, which makes it suitable for high-speed-high-capacity optical communication systems.     

An optical fiber chemical sensor for mercury ions based on a porphyrin dimer

The synthesis of a novel fluoroionophore, 5-p-[[4-(10',15',20'-triphenyl-5'-porphinato) phenyloxyl]-1-butyloxyl]phenyl-10,15,20-triphenylporphine (DTPP), and its application for preparation of a Hg(II)-sensitive optical fiber chemical sensor are described. The response of the sensor is based on the fluorescence quenching of DTPP by coordination with Hg(II). The porphyrin dimer-based sensor shows a linear response toward Hg(II) in the concentration range 5.2 x 10(-7)-3.1 x 10(-4) mol x L(-1), with a working pH range from 2.4 to 8.0. The sensor shows excellent selectivity for Hg(II) over transition metal cations including Cd(II), Co(II), Cu(II), Ni(II), Pb(II), Zn(II), and Fe(III). As a sensing agent, the porphyrin dimer shows obviously better fluorescence response characteristics toward Hg(II) compared to porphyrin monomer or metalloporphyrin. The effect of the composition of the sensor membrane was studied, and the experimental conditions were optimized. The sensor has been used for determination of Hg(II) in water samples.     

Selective determination of beryllium(II) ion at picomole per decimeter cubed levels by kinetic differentiation mode reversed-phase high-performance liquid chromatography with fluorometric detection using 2-(2'-hydroxyphenyl)-10-hydroxybenzo[H]quinoline as precolumn chelating reagent

A highly sensitive and selective method for the determination of the Be(II) ion has been developed by the use of reversed-phase high-performance liquid chromatography (HPLC) with fluorometric detection using 2-(2'-hydroxyphenyl)-10-hydroxybenzo[h]quinoline (HPHBQ) as a precolumn (off-line) chelating reagent. The reagent HPHBQ has been designed to form the kinetically inert Be chelate compatible with high fluorescence yield, which is appropriate to the HPLC-fluorometric detection system. The Be-HPHBQ chelate is efficiently separated on a LiChrospher 100 RP-18(e) column with a methanol (58.3 wt %)-water eluent containing 20 mmol kg(-1) of tartaric acid and is fluorometrically detected at 520 nm with the excitation at 420 nm. Under the conditions used, the concentration range of 20-8,000 pmol dm(-3) of Be(II) ion can be determined without interferences from 10 micromol dm(-3) each of common metal ions, typically Al(III), Cu(II), Fe(III), and Zn(II), and still more coexistence of Ca(II) and Mg(II) ions at 0.50 mmol dm(-3) and 5.0 mmol dm(-3), respectively, is tolerated. The detection limit (3a baseline fluctuation) is 4.3 pmol dm(-3) (39 fg cm(-3)). The extraordinarily high sensitivity with toughness toward the matrix influence was demonstrated with the successful application to environmental Be analyses, such as determination of Be in rainwater and tap water.     

Preconcentration and determination of trace metal ions from aqueous samples by newly developed gallic acid modified Amberlite XAD-16 chelating resin

Gallic acid was immobilized on Amberlite XAD-16 by coupling it through -N=N group. The resulting chelating resin Amberlite XAD-16 gallic acid, characterized by thermogravimetric analysis (TGA), infrared (IR) spectra and BET analysis, was used to preconcentrate Cr(III), Mn(II),Fe(III),Co(II), Ni(II) and Cu(II)ions. The resin was employed for the preconcentration of the metal ions present in river water and industrial area aqueous samples. Several parameters like effect of pH, effect of time, effect of sample volume and flow rate of sample were investigated. The sorption capacities for the resin were 216 micromol g(-1), 180 micromol g(-1), 403 micromol g(-1), 281 micromol g(-1), 250 micromol g(-1) and 344 micromol g(-1) for Cr(III), Mn(II), Fe(III), Co(II), Ni(II) and Cu(II) respectively. The preconcentration factors for Cr(III), Mn(II), Fe(III), Ni(II), Co(II) and Cu(II) were found out to be 300, 200, 400, 285.7, 300 and 400 respectively. The effect of various interfering ions was also studied. Results were validated by using standard addition method for river water sample.     

Preconcentration of Pb(II), Cr(III), Cu(II), Ni(II) and Cd(II) ions in environmental samples by membrane filtration prior to their flame atomic absorption spectrometric determinations

A method for separation-preconcentration of Pb(II), Cr(III), Cu(II), Ni(II) and Cd(II) ions by membrane filtration has been described. The method based on the collection of analyte metal ions on a cellulose nitrate membrane filter and determination of analytes by flame atomic absorption spectrometry (FAAS). The method was optimized for several parameters including of pH, matrix effects and sample volume. The recoveries of analytes were generally in the range of 93-100%. The detection limits by 3 sigma for analyte ions were 0.02microgL(-1) for Pb(II), 0.3microgL(-1) for Cr(III), 3.1microgL(-1) for Cu(II), 7.8microgL(-1) for Ni(II) and 0.9microgL(-1) for Cd(II). The proposed method was applied to the determination of lead, chromium, copper, nickel and cadmium in tap waters and RM 8704 Buffalo River Sediment standard reference material with satisfactory results. The relative standard deviations of the determinations were below 10%.     

Magnetic nanobiosorbent (MG‐Chi/Fe3O4) for dispersive solid‐phase extraction of Cu(II), Pb(II), and Cd(II) followed by flame atomic absorption spectrometry determination

Trace amounts of Cu (II), Pb (II), and Cd (II) in a wastewater sample were preconcentrated with a novel cross‐linked magnetic chitosan modified with a new synthesised methionine‐glutaraldehyde Schiff''s base (MG‐Chi/Fe₃O₄) as a dispersive solid‐phase extraction (DSPE) adsorbent. The adsorbed metal ions were then eluted with a specific volume of suitable solution and determined by flame atomic absorption spectrometry (FAAS). Various parameters affecting the extraction efficiency of the metal ions were investigated and optimised, including pH, amount of adsorbent, extraction time, type and volume rate of eluent, elution time, sample volume, and effect of interfering ions. The adsorption kinetics are more consistent with the pseudo‐second order model. The results were statistically interpreted and the analytical performance of the proposed method was found to have preconcentration factors of 55, 60, and 50 μg L⁻¹ for Cu(II), Pb(II), and Cd(II), respectively, limits of detection were 0.22, 0.24, and 0.10 μg L⁻¹ for Cu(II), Pb(II), and Cd(II), respectively, with a relative standard deviation (1.5%‐2.8 %), and the liner range was 5–1000 for Cu(II) and Pb(II) and 2.5–1000 for Cd(II). It was concluded that this method was suitable for successful simultaneous determination of Cu(II), Pb(II), and Cd(II) in industrial wastewater samples.     

Complexing of heavy metals with DNA and new bioaffinity method of their determination based on amperometric DNA-based biosensor

The immobilized single-stranded DNA (ssIDNA) has been found to be a very effective biospecific analytical reagent when used in a newly developed bioaffinity method of the determination of heavy metals based on the amperometric DNA-based biosensor. This has been concluded from the comparative study of the complexing of heavy metals with double-stranded DNA, single-stranded DNA, and ssIDNA, using Fe(III) and Cu(II) as a model (metal/nucleotide ratio and stability constants are maximum for ssIDNA), from the study of adsorption of Fe(III), Cu(II), Pb(II), and Cd(II) on nitrocellulose membranes, containing single-stranded DNA, and from the determination of their binding constants with ssIDNA. According to these data, the chosen heavy metals can be lined up in a series of binding strengths with ssIDNA: Cu(II) > Pb(II) > Fe(III) > Cd(II). The method of the determination of heavy metals is based on biospecific preconcentration of metal ions on the biosensor followed by the destruction of DNA-metal complexes with ethylenediaminetetraacetate and voltammogram recording has been proposed. The lower detection limits are 4.0 x 10(-11), 1.0 x 10(-10), 1.0 x 10(-9), and 5.0 x 10(-9) M for Cu(II), Pb(II), Cd(II), and Fe(III), respectively. The heavy metals have been assayed in multicomponent environmental and biological systems such as natural and drinking water, milk, and blood serum samples.     

Preconcentration and solid phase extraction method for the determination of Co, Cu, Ni, Zn and Cd in environmental and biological samples using activated carbon by FAAS

2-{[1-(2-Hydroxynaphthyl) methylidene] amino} benzoic acid (HNMABA) was synthesized for solid phase extraction (SPE) to the determination of Co, Cu, Ni, Zn and Cd in environmental and biological samples by flame atomic absorption spectrophotometry (FAAS). These metals were sorbed as HNMABA complexes on activated carbon (AC) at the pH range of 5.0+/-0.2 and eluted with 6 ml of 1M HNO3 in acetone. The effects of sample volume, eluent volume and recovery have been investigated to enhance the sensitivity and selectivity of proposed method. The effect of interferences on the sorption of metal ions was studied. The concentration of the metal ions detected after preconcentration was in agreement with the added amount. The detection limits for the metals studied were in the range of 0.75-3.82 microg ml(-1). The proposed system produced satisfactory results for the determination of Co, Cu, Ni, Zn and Cd metals in environmental and biological samples.     

Real-time determination of picomolar free Cu(II) in seawater using a fluorescence-based fiber optic biosensor

We report real-time, in situ determination of free copper ion at picomolar levels in seawater using a fluorescence-based fiber optic biosensor. The sensor transducer is a protein molecule, site-specifically labeled with a fluorophore that is attached to the distal end of an optical fiber, which binds free Cu(II) with high affinity and selectivity. The transducer reports the metal's concentration as a change in fluorescence intensity or lifetime, using a frequency domain approach. The transducer's response time is diffusion-limited, with a typical measurement requiring 30 s. The sensor demonstrates a detection limit of 0.1 pM free Cu(II) in a seawater model. Accuracy and precision of the sensor were at least comparable to cathodic ligand exchange/adsorptive cathodic stripping voltammetry. Measurements of tidal flushing of a copper-contaminated inlet are shown.     

On-line preconcentration of copper as its pyrocatechol violet complex on Chromosorb 105 for flame atomic absorption spectrometric determinations

An on-line solid phase extraction method for the preconcentration and determination of Cu(II) by flame atomic absorption spectrometry (FAAS) has been described. It is based on the adsorption of copper(II) ion onto a home made mini column of Chromosorb 105 resin loaded with pyrocatechol violet at the pH range of 5.0-8.0, then eluted with 1 mol L(-1) HNO(3). Several parameters, such as pH of the sample solution, amount of Chromosorb 105 resin, volume of sample and eluent, type of eluent, flow rates of sample and eluent, governing the efficiency and throughput of the method were evaluated. The concentration of the copper ion detected after preconcentration was in agreement with the added amount. At optimized conditions, for 15 min of preconcentration time (30 mL of sample volume), the system achieved a detection limit of 0.02 microg L(-1), with relative standard deviation 1.1% at 0.03 microg mL(-1) copper. The present method was found to be applicable to the preconcentration of Cu(II) in natural water samples.     

Automated two-column ion exchange system for determination of the speciation of trace metals in natural waters

A rapid method for determination of metal speciation based on an automated two-column ion exchange system is described. Two fractions of dissolved trace metal species are directly determined by on-line flame atomic absorption spectrophotometry after preconcentration by sequential columns of Chelex-100 chelating resin and AG MP-1 macroporous anion resin. A third fraction is determined by standard addition. Variables that affect the results obtained by the two-column system are studied by the use of model complexing agents. With a 10-mL sample loop, the sample throughput is 6 samples per hour and detection limits are 0.1 micrograms/L for Cu(II), 0.08 micrograms/L for Cd(II), and 0.2 micrograms/L for Zn(II). The method is used to determine the speciation of Cu(II), Cd(II), and Zn(II) in natural water samples.     

Zincon-modified activated carbon for solid-phase extraction and preconcentration of trace lead and chromium from environmental samples

A new method that utilizes zincon-modified activated carbon (AC-ZCN) as a solid-phase extractant has been developed for simultaneous preconcentration of trace Cr(III) and Pb(II) prior to the measurement by inductively coupled plasma optical emission spectrometry (ICP-OES). The separation/preconcentration conditions of analytes were investigated, including effects of pH, the shaking time, the sample flow rate and volume, the elution condition and the interfering ions. At pH 4, the maximum adsorption capacity of Cr(III) and Pb(II) onto the AC-ZCN were 17.9 and 26.7 mg g⁻¹, respectively. The adsorbed metal ions were quantitatively eluted by 1 mL of 0.1 mol L⁻¹ HCl. Common coexisting ions did not interfere with the separation. According to the definition of IUPAC, the detection limits (3σ) of this method for Cr(III) and Pb(II) were 0.91 and 0.65 ng mL⁻¹, respectively. The relative standard deviation under optimum condition is less than 3.5% (n = 8). The method has been applied for the determination of Cr(III) and Pb(II) in biological materials and water samples with satisfactory results.     

SP70-alpha-benzoin oxime chelating resin for preconcentration-separation of Pb(II), Cd(II), Co(II) and Cr(III) in environmental samples

In the presented work, alpha-benzoin oxime immobilized SP70 chelating resin was synthesized for separation and preconcentration of Pb(II), Cd(II), Co(II) and Cr(III). The optimization procedure for analytical parameters including pH, eluent type, flow rate, etc. was examined in order to gain quantitative recoveries of analyte ions. The effects of foreign ions on the recoveries of studied metal ions were also investigated. The detection limits (3sigma) were found to be 16.0, 4.2, 1.3, 2.4microgL(-1) for Pb, Cd, Co and Cr, respectively. The preconcentration factor was 75 for Pb, 100 for Cd, Co and Cr. The optimized method was validated with certified reference materials and successfully applied to the waters, crops and pharmaceutical samples with good results (recoveries greater than 95%, R.S.D. lower than 10%).     

Copper ion-selective fluorescent sensor based on the inner filter effect using a spiropyran derivative

A highly selective copper(II) ion fluorescent sensor has been designed based on the UV-visible absorption of a spiropyran derivative coupled with the use of a metal porphyrin operative on the fluorescence inner filter effect. Spiropyrans, which combine the characteristics of metal binding and signal transduction, have been widely utilized in cationic ion recognition by UV-visible spectroscopy. In the present work, the viability of converting the absorption signal of the spiropyran molecule into a fluorescence signal was explored. On account of overlap of the absorption band of the spiropyran (lambda(abs) = 547 nm) in the presence of copper ion with the Q-band of an added fluorophore, zinc meso-tetraphenylporphyrin (lambda(abs) = 556 nm), the effective light absorbed by the porphyrin and concomitantly the emitted light intensity vary as a result of varying absorption of the spiropyran via fluorescence inner filter effect. The metal binding characteristic of the spiropyran presents an excellent selectivity for copper ion in comparison with several other heavy or transition metal ions. Since the changes in the absorbance of the absorber translate into exponential changes in fluorescence of the fluorophore, the novelty of the present device is that the analytical signal is more sensitive over that of the absorptiometry or that of the fluorometry using one single dye. To realize a practical fluorescent sensor, both the absorber and fluorophore were immobilized in a plasticized poly(vinyl chloride) membrane, and the sensing characteristics of the membrane for copper ion were investigated. The sensor is useful for measuring Cu2+ at concentrations ranging from 7.5 x 10(-7) to 3.6 x 10(-5) M with a detection limit of 1.5 x 10(-7) M. The sensor is chemically reversible, the fluorescence was switched off by immersing the membrane in copper ion solution and switched on by washing it with EDTA solution.