Application of artificial neural network to simultaneous potentiometric determination of silver(I), mercury(II) and copper(II) ions by an unmodified carbon paste electrode

The response characteristics and selectivity coefficients of an unmodified carbon paste electrode (CPEs) towards Ag⁺, Cu²⁺ and Hg²⁺ were evaluated. The electrode was used as an indicator electrode for the simultaneous determination of the three metal ions in their mixtures via potentiometric titration with a standard thiocyanate solution. A three-layered feed-forward artificial neural network (ANN) trained by back-propagation learning algorithm was used to model the complex non-linear relationship between the concentration of silver, copper and mercury in their different mixtures and the potential of solution at different volumes of the added titrant. The network architecture and parameters were optimized to give low prediction errors. The optimized networks were able to precisely predict the concentrations of the three cations in synthetic mixtures.     

Synthesis of Cu-mediated nano-sized salbutamol-imprinted polymer and its use for indirect recognition of ultra-trace levels of salbutamol

Cu²⁺-mediated salbutamol-imprinted polymer nanoparticles, synthesized by precipitation polymerization, were mixed with graphite powder and n-eicosane in order to fabricate a modified carbon paste electrode. This electrode was then applied for indirect differential pulse voltammetry determination of salbutamol. In the presence of Cu²⁺ ions, the formed Cu²⁺–salbutamol complex was adsorbed in to the pre-designed cavities of the MIP particles, situated on the electrode surface. Since the electrochemical signal of salbutamol was intrinsically small, the oxidation peak of the participant Cu²⁺, after reduction step, was recorded and used as an indication of salbutamol amount, adsorbed in the electrode. Different variables influencing the sensor performance were studied and the best conditions were chosen for the determination purpose. Correlation between the sensor response to salbutamol and its concentration was linear in the range of 1.0 × 10⁻⁹–5.5 × 10⁻⁸ M. Detection limit was calculated equal to 6.0 × 10⁻¹⁰ M (S/N). Five replicated determination of salbutamol (1 × 10⁻⁸ M) resulted in standard error of 3.28%, meaning a satisfactory precision of the determination method. The prepared sensor was applied for real sample analysis. In order to minimize the interference effect, the synthesized polymer was successfully used as a solid phase sorbent for salbutamol extraction, before analysis of real samples by the developed sensor.     

Determination of Hg on poly(vinylferrocenium) (PVF)-modified platinum electrode

A new surface based on poly(vinylferrocenium) (PVF⁺)-modified platinum electrode was developed for determination of Hg²⁺ ions in aqueous solutions. The polymer was electrodeposited on platinum electrode by constant potential electrolysis as PVF⁺ClO₄⁻. Cl⁻ ions were then attached to the polymer matrix by anion exchange and the modified electrode was dipped into Hg²⁺ solution. Hg²⁺ was preconcentrated at the polymer matrix by adsorption and also complexation reaction with Cl⁻. Detection of Hg²⁺ was carried out by differential pulse anodic stripping voltammetry (DPASV) after reduction of Hg²⁺. Mercury ions as low as 5 × 10⁻¹⁰ M could be detected with the prepared electrode and the relative standard deviation was calculated as 6.35% at 1 × 10⁻⁶ M concentration (n = 6). Interferences of Ag⁺, Pb²⁺ and Fe³⁺ ions were also studied at two different concentration ratios with respect to Hg²⁺. The developed electrode was applied to the determination of Hg²⁺ in water samples.     

Photoactive chemosensors 4: a Cu protein cavity mimicking fluorescent chemosensor for selective Cu recognition

Fluorescent chemosensor 3 can sense Cu²⁺ ions (1-8 μM) even in the presence of elevated levels of Ni²⁺, Cd²⁺, Zn²⁺, Hg²⁺, Ag⁺ and Pb²⁺ (5000 μM). 3 can also analyze for Ag⁺ ions (50-500 μM) in the presence of Ni²⁺, Cd²⁺, Zn²⁺, Hg²⁺ and Pb²⁺ (5000 μM) but Cu²⁺ strongly interferes.     

Probing trace Pb(2+) using electrodeposited N,N'-(o-phenylene)-bis-benzenesulfonamide polymer as a novel selective ion capturing film

A novel film modified electrode for the determination of trace lead was developed in this work. The modified electrode was prepared by the electropolymerization of N,N′-(o-phenylene)-bis-benzenesulfonamide (PBSA) as the ion capturing reagent to create the functional film. The modified electrode shows a high selectivity towards Pb²⁺ over interfering cations, e.g. Cu²⁺, Cd²⁺, Co²⁺, Ni²⁺, Zn²⁺, Cr²⁺, and the calibration curve was linear in the concentration range of 2.0 × 10⁻⁹ to 1.0 × 10⁻⁷ M with correlation coefficient of 0.999. For 20 min accumulation, detection limit of 1.0 × 10⁻⁹ M was obtained at the signal to noise ratio of 3. Analytical availability of the modified electrode was demonstrated by the application for samples from pond water.     

Sodium polyacrylate as a binding agent in diffusive gradients in thin-films technique for the measurement of Cu and Cd in waters

An aqueous solution containing sodium polyacrylate (PA, 0.0030 M) was used in diffusive gradients in thin-films technique (DGT) to measure DGT-labile Cu²⁺ and Cd²⁺ concentrations. The DGT devices (PA DGT) were validated in four types of solutions, including synthetic river waters containing metal ions with or without complexing EDTA, natural river water (Hun River, Shenyang, China) spiked with Cu²⁺ and Cd²⁺, and an industrial wastewater (Shenyang, China). Results showed that only free metal ions were measured by PA DGT, recovery = 98.79% for Cu²⁺ and recovery = 97.80% for Cd²⁺ in solutions containing only free metal ions, recovery = 51.02% for Cu²⁺ and recovery = 51.92% for Cd²⁺ in solution with metal/EDTA molar ratio of 2:1 and recovery = 0 in solutions with metal/EDTA molar ratio of 1:1 and 1:2. These indicated that the complexes of Cu-EDTA and Cd-EDTA were DGT-inert or not DGT-labile. The DGT performance in spiked river water (recovery = 8.47% for Cu²⁺ and recovery = 27.48% for Cd²⁺) and in industrial wastewater (recovery = 14.16% for Cd²⁺) were also investigated. Conditional stability constants (log K) of PA-Cu and PA-Cd complexes were determined as 6.98 and 5.61, respectively, indicating strong interaction between PA and the metals.     

A novel colorimetric and fluorescent chemosensor: synthesis and selective detection for Cu and Hg

A novel two-channel metal ion sensor has been synthesized from macrocyclic dioxotetraamine and 1,8-naphthalimide derivative. The metal ion-selective signaling behaviors of the sensor were investigated. The sensor presented the selective coloration for Cu²⁺ and Hg²⁺ that can be detected by the naked-eye, respectively. Besides, the addition of Cu²⁺ and Hg²⁺ quenched the fluorescence of 1 obviously and the detection limit was found to be 3 × 10⁻⁷ M for Cu²⁺ and 7 × 10⁻⁷ M for Hg²⁺. This sensor can be utilized for the visual and spectroscopic detection of Cu²⁺ or Hg²⁺ in the presence of the other competing metal ions.     

Dimethylcyclam based fluoroionophore having Hg- and Cd-selective signaling behaviors

Diametrically disubstituted bis(anthrylmethyl) derivative of 1,8-dimethylcyclam exhibited pronounced Hg²⁺- and Cd²⁺-selective fluorogenic behaviors in aqueous acetonitrile solution. A distinctive OFF-ON type signaling was observed for Hg²⁺ and Cd²⁺ ions in aqueous acetonitrile (CH₃CN-H₂O = 90:10, v/v) solution, while a selective ON-OFF type switching behavior toward Hg²⁺ ions was observed in solution having higher water content (CH₃CN-H₂O = 50:50, v/v). The detection limit for the analysis of Hg²⁺ ions in 50% aqueous acetonitrile was found to be 3.8 × 10⁻⁶ M. The selective OR logic gate behavior of the prepared compound toward two toxic heavy metal ions of Hg²⁺ and Cd²⁺ ions in CH₃CN-H₂O (90:10, v/v) suggests the possibility as a new chemosensing device for the two important target metal ions.     

Hg- and Cu-selective fluoroionophoric behaviors of a dioxocyclam derivative bearing anthrylacetamide moieties

New dioxocyclam derivatives bearing two anthracene fluorophores were prepared, and their fluoroionophoric properties toward transition metal ions were investigated. Chemosensor 2 having anthrylacetamide moieties exhibited pronounced Hg²⁺- and Cu²⁺-selective fluoroionophoric properties in aqueous acetonitrile solution over other representative transition metal ions, as well as alkali and alkaline earth metal ions. Chemosensor 2 also exhibited Hg²⁺ and Cu²⁺ selectivity under competitive conditions in the presence of physiologically and environmentally important metal ions. The detection limits for the sensing of Hg²⁺ and Cu²⁺ ions were 7.8 × 10⁻⁶ and 1.5 × 10⁻⁶ M, respectively, in aqueous 95% acetonitrile solution.     

Non-conductive nanomaterial enhanced electrochemical response in stripping voltammetry: The use of nanostructured magnesium silicate hollow spheres for heavy metal ions detection

Nanostructured magnesium silicate hollow spheres, one kind of non-conductive nanomaterials, were used in heavy metal ions (HMIs) detection with enhanced performance for the first time. The detailed study of the enhancing electrochemical response in stripping voltammetry for simultaneous detection of ultratrace Cd²⁺, Pb²⁺, Cu²⁺ and Hg²⁺ was described. Electrochemical properties of modified electrodes were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The operational parameters which have influence on the deposition and stripping of metal ions, such as supporting electrolytes, pH value, and deposition time were carefully studied. The anodic stripping voltammetric performance toward HMIs was evaluated using square wave anodic stripping voltammetry (SWASV) analysis. The detection limits achieved (0.186 nM, 0.247 nM, 0.169 nM and 0.375 nM for Cd²⁺, Pb²⁺, Cu²⁺ and Hg²⁺) are much lower than the guideline values in drinking water given by the World Health Organization (WHO). In addition, the interference and stability of the modified electrode were also investigated under the optimized conditions. An interesting phenomenon of mutual interference between different metal ions was observed. Most importantly, the sensitivity of Pb²⁺ increased in the presence of certain concentrations of other metal ions, such as Cd²⁺, Cu²⁺ and Hg²⁺ both individually and simultaneously. The proposed electrochemical sensing method is thus expected to open new opportunities to broaden the use of SWASV in analysis for detecting HMIs in the environment.     

Naked-eye colorimetric analysis of Hg2+ with bi-color CdTe quantum dots multilayer films

A novel direct quantificational method through naked-eye colorimetric analysis of Hg²⁺ was constructed based on different degree of the fluorescence quenching of bi-color quantum dots (QDs) multilayer films (2-QDMF). The functional multilayer films were assembled by layer-by-layer (LBL) deposition of oppositely charged CdTe QDs and poly(dimethyldiallylemmonium chloride) (PDDA). Then the outermost layer of 2-QDMF was cross-linked to bovine serum albumin (BSA), polyethylene glycol (PEG) or glutathione (GSH). It was found that when BSA modified quartz slides were immersed into solutions containing Hg²⁺ and Cu²⁺ respectively, the 2-QDMF can be quenched by Hg²⁺, but not by Cu²⁺. Under the optimization conditions, the quenched photoluminescence (PL) intensities of multilayer films were almost linearly proportional to the concentration of Hg²⁺ in the range of 1.0 × 10⁻⁸ to 1.0 × 10⁻⁶ mol L⁻¹ and the detection limit was 4.5 × 10⁻⁹ mol L⁻¹. The proposed method is intuitional and convenient, which can be applied to the determination of trace Hg²⁺ in the artificial water sample with satisfactory results.     

Electrodes with extremely high hydrogen overvoltages as substrate electrodes for stripping analysis based on bismuth-coated electrodes

Hydrogen evolution bothers stripping analysis significantly. Dioctyl phthalate-based carbon paste electrode exhibits extremely wide cathodic potential window. It is explored as a powerful substrate electrode to solve the problem of hydrogen evolution and further improve reproducibility for stripping analysis using bismuth-coated electrodes for the first time. It was successfully applied to the simultaneous determination of Zn²⁺, Cd²⁺, and Pb²⁺. Linear responses are obtained for Zn²⁺ in the range of 10–100 μg L⁻¹ and for Pb²⁺ and Cd²⁺ in the range of 5–100 μg L⁻¹. The detection limits for Zn²⁺, Cd²⁺, and Pb²⁺ are 0.1 μg L⁻¹, 0.22 μg L⁻¹ and 0.44 μg L⁻¹, respectively. The method has been successfully applied to the determination of Zn²⁺, Cd²⁺, and Pb²⁺ in waste water samples. The detection strategy based on the combination of dioctyl phthalate-based carbon paste electrode and bismuth-coated electrodes holds great promise for stripping analysis.     

A highly selective pyrene based fluorescent sensor toward Hg detection

A new pyrene-containing fluorescent sensor has been synthesized from 2,3,3-trimethylindolenine. Spectroscopic and photophysical properties of sensor are presented. The large change in fluorescence intensity (I/I₀ = 0.13) at 381 nm and affinity to Hg²⁺ over other cations such as K⁺, Na⁺, Ca²⁺, Mg²⁺, Pb²⁺, and Cu²⁺ make this compound a useful chemosensor for Hg²⁺ detection in hydrophilic media. The sensor (6.0 × 10⁻⁶ M) displays significant fluorescence quenching upon addition of Hg²⁺ in pH 7.4 HEPES buffer without excimer formation. Job’s plot analysis shows the binding stoichiometry to be 2:1 (host/guest).     

Simultaneous determination of lead(II) and cadmium(II) at a diacetyldioxime modified carbon paste electrode by differential pulse stripping voltammetry

A simple and effective chemically modified carbon paste electrode (CMCPE) for the simultaneous determination of lead(II) and cadmium(II) was developed in this work. The electrode was prepared by the addition of diacetyldioxime into a carbon paste mixture. Pb²⁺ and Cd²⁺ were preconcentrated on the surface of the modified electrode by complexing with diacetyldioxime and reduced at a negative potential (−1.10 V). Then the reduced products were oxidized by differential pulse stripping. The fact that two stripping peaks appeared on the voltammograms at the potentials of −0.65 V (Cd²⁺) and −0.91 V (Pb²⁺) demonstrates the possibility of simultaneous determination of Pb²⁺ and Cd²⁺. Under the optimized working conditions, calibration graphs were linear in the concentration ranges of 1.0×10⁻⁷-1.5×10⁻⁵ mol l⁻¹ (Pb²⁺) and 2.5×10⁻⁷-2.5×10⁻⁵ mol l⁻¹ (Cd²⁺), respectively. For 5 min preconcentration, detection limits of 1×10⁻⁸ mol l⁻¹ (Pb²⁺) and 4×10⁻⁸ mol l⁻¹ (Cd²⁺) were obtained at the signal noise ratio (SNR) of 3. To evaluate the reproducibility of the newly developed electrode, the measurements of 5×10⁻⁷ mol l⁻¹ Pb²⁺ and Cd²⁺ were parallel carried out for six times at different electrodes and the relative standard deviations were 2.9% (Pb²⁺) and 3.2% (Cd²⁺), respectively. Interferences by some metals were investigated. Only Ni²⁺ and Hg²⁺ apparently affected the peak currents of Pb²⁺ and Cd²⁺. The diacetyldioxime modified carbon paste electrode was applied to the determination of Pb²⁺ and Cd²⁺ in water samples. The results indicate that this electrode is sensitive and effective for the simultaneous determination of Pb²⁺ and Cd²⁺.     

Characterization and application of humic acid modified carbon electrodes

Four routes for the modification of carbon electrodes with humic acids and the determination of three divalent metallic cations were studied. The determination of bound Fe²⁺, Cu²⁺ and Ni²⁺ was performed by cyclic and square wave voltammetry using either a batch or flow analysis system. Using the FIA system and SWV, linear relationships between the oxidation (or reduction) current and the cations concentration were obtained with the modified electrodes, while no signals were obtained for the same conditions for bare carbon electrodes. The system can be used to study the interaction between a wide range of electroactive cations and humic substances; however, the performance as an analytical tool is limited due to the high limits of detection (μM). However, some advantages like simplicity, short analysis time, inexpensive instrumentation needs and miniaturization capabilities are remarkable.     

Simultaneous detection of cadmium, copper, and lead using a carbon paste electrode modified with carbamoylphosphonic acid self-assembled monolayer on mesoporous silica (SAMMS)

A new sensor was developed for simultaneous detection of cadmium (Cd²⁺), copper (Cu²⁺), and lead (Pb²⁺), based on the voltammetric response at a carbon paste electrode modified with carbamoylphosphonic acid (acetamide phosphonic acid) self-assembled monolayer (SAM) on mesoporous silica (Ac-Phos SAMMS). The adsorptive stripping voltammetry (AdSV) technique involves preconcentration of the metal ions onto Ac-Phos SAMMS under an open circuit, then electrolysis of the preconcentrated species, followed by a square wave potential sweep towards positive values. Factors affecting the preconcentration process were investigated. The voltammetric responses increased linearly with the preconcentration time from 1 to 30 min or with metal ion concentrations ranging from 10 to 200 ppb. The responses also evolved in the same fashion as adsorption isotherm in the pH range of 2-6. The metal detection limits were 10 ppb after 2 min preconcentration and improved to 0.5 ppb after 20 min preconcentration.     

A new fluorescent sensor bearing three dansyl fluorophores for highly sensitive and selective detection of mercury(II) ions

A novel fluorometric sensor bearing three dansyl moieties based on tris[2-(2-aminoethylthio)ethyl]amine was prepared by a simple approach using a conventional two-step synthesis. The sensor exhibits highly Hg²⁺-selective ON-OFF fluorescence quenching behavior in aqueous acetonitrile solutions and is shown to discriminate various competing metal ions, particularly Cu²⁺, Ag⁺, and Pb²⁺ as well as Ca²⁺, Cd²⁺, Co²⁺, Fe³⁺, Mn²⁺, Na⁺, Ni²⁺, and Zn²⁺, with a detection limit of 1.15 × 10⁻⁷ M or 23 ppb.     

Simultaneous trace-levels determination of Hg(II) and Pb(II) ions in various samples using a modified carbon paste electrode based on multi-walled carbon nanotubes and a new synthesized Schiff base

A modified carbon paste electrode based on multi-walled carbon nanotubes (MWCNTs) and 3-(4-methoxybenzylideneamino)-2-thioxothiazolodin-4-one as a new synthesized Schiff base was constructed for the simultaneous determination of trace amounts of Hg(II) and Pb(II) by square wave anodic stripping voltammetry. The modified electrode showed an excellent selectivity and stability for Hg(II) and Pb(II) determinations and for accelerated electron transfer between the electrode and the analytes. The electrochemical properties and applications of the modified electrode were studied. Operational parameters such as pH, deposition potential and deposition time were optimized for the purpose of determination of traces of metal ions at pH 3.0. Under optimal conditions the limits of detection, based on three times the background noise, were 9.0 × 10⁻⁴ and 6.0 × 10⁻⁴ μmol L⁻¹ for Hg(II) and Pb(II) with a 90 s preconcentration, respectively. In addition, the modified electrode displayed a good reproducibility and selectivity, making it suitable for the simultaneous determination of Hg(II) and Pb(II) in real samples such as sea water, waste water, tobacco, marine and human teeth samples.     

Complexation of metal ions with the novel azathia crown ethers carrying anthracene pendant in acetonitrile–dichloromethane

A series of crown ethers carrying an anthracene group with nitrogen–sulfur donor atom, which differ in having three, four and five sulfur atoms in the macrocycle was designed and synthesized by the reaction of the corresponding macrocyclic compound and 9-chloromethyl-anthracene. The influence of metal cations such as Al³⁺, Zn²⁺, Fe²⁺, Fe³⁺, Co²⁺, Ni²⁺, Mn²⁺, Cu²⁺, Cd²⁺, Hg²⁺ and Pb²⁺ on the spectroscopic properties of the ligands was investigated in acetonitrile–dichloromethane (1:1) by means of absorption and emission spectrometry. Absorption spectra show isosbestic points in the spectrophotometric titration of Al³⁺, Zn²⁺, Fe²⁺, Fe³⁺, Cu²⁺, Hg²⁺ and Pb²⁺ the results of which disclosed the complexation compositions and complex stability constants of the novel ligands with these cations. The monoazapentathia crown ether showed sensitivity for Al³⁺ with linear range and detection limit of 2.6 × 10⁻⁶ M–2.6 × 10⁻⁵ M and 8.1 × 10⁻⁷ M, respectively.     

Conductometric studies and application of new Schiff base ligand as carbon paste electrode modifier for mercury and cadmium determination

A new chemically modified carbon paste electrode by 2,2?-((pyridine-2,6-diylbis(azanylylidene))bis(methanylylidene))diphenol (L) ligand has been made and used as a sensor for determination of trace mercury and cadmium ions with cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods. Complexation studies of the ligand with Cu²⁺, Zn²⁺, Hg²⁺, Ni²⁺ and Cd²⁺ ions by conductometric method in acetonitrile–ethanol mixture at 25°C show that the ML complexes have formed. The formation constants of complexes were calculated from the computer fitting of the molar conductance–mole ratio data, and the stability of the resulting complexes varied in order of Cd²⁺ > Hg²⁺ > Cu²⁺ > Zn²⁺ > Ni²⁺. Then a simple and effective chemically modified carbon paste electrode with L was prepared, and the electrochemical properties and applications of the modified electrode were investigated. Under the optimal conditions, the detection limit was 0.0494 μg L^?1 and 0.0782 μg L^?1 for cadmium and mercury ions, respectively, and the linear range for both metal ions were from 1 to 100 μg L^?1. The electrode shows high sensitivity, reproducibility and low cost, and was successfully applied to determination of Cd²⁺ and Hg²⁺ ions in water samples with recovery in the range of 97–101%.