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%.     

Evaluation of a novel composite based on functionalized multi-walled carbon nanotube and iron phthalocyanine for electroanalytical determination of isoniazid

A novel platform for electroanalysis of isoniazid based on graphene-functionalized multi-walled carbon nanotube as support for iron phthalocyanine (FePc/f-MWCNT) has been developed. The FePc/f-MWCNT composite has been dropped on glassy carbon forming FePc/f-MWCNT/GC electrode, which is sensible for isoniazid, decreasing substantially its oxidation potential to +200 mV vs Ag/AgCl. Electrochemical and electroanalytical properties of the FePc/f-MWCNT/GC-modified electrode were investigated by cyclic voltammetry, electrochemical impedance spectroscopy, scanning electrochemical microscopy, and amperometry. The sensor presents better performance in 0.1 mol L^?1 phosphate buffer at pH 7.4. Under optimized conditions, a linear response range from 5 to 476 μmol L^?1 was obtained with a limit of detection and sensitivity of 0.56 μmol L^?1 and 0.023 μA L μmol^?1, respectively. The relative standard deviation for 10 determinations of 100 μmol L^?1 isoniazid was 2.5%. The sensor was successfully applied for isoniazid selective determination in simulated body fluids.     

Application of horseradish peroxidase/polyaniline/bis(2-aminoethyl) polyethylene glycol-functionalized carbon nanotube composite as a platform for hydrogen peroxide detection with high sensitivity at low potential

Polyaniline/O,O′-bis (2-aminoethyl) polyethylene glycol-functionalized multiwalled carbon nanotube (PANI/PEG–MWCNT) composite-modified electrode was successfully prepared by electropolymerization. The ionic transport in PANI/PEG–MWCNT film and its effects on the composite performance are presented. Both protonic and anionic participation in the charge compensation processes were calculated and they indicated that the presence of the PEG–MWCNT in the PANI film suppress the anionic transportation and improve the composite ability in fixing horseradish peroxidase enzyme. Finally, the adsorption between the negatively charged PANI/PEG–MWCNT nanocomposite and the positively charged Horseradish peroxidase resulted in a high sensitivity (1.01 μA L cm^?2 μmol^?1) to hydrogen peroxide. This sensor exhibited a good reproducibility and stability at an applied potential of ?100 mV vs Ag/AgCl.     

Enhanced Specificity and Sensitivity for the Determination of Nickel(II) by Square-wave Adsorptive Cathodic Stripping Voltammetry at Disposable Graphene-modified Pencil Graphite Electrodes

Chemical sensors relying on graphene-based materials have been widely used for electrochemical determination of metal ions and have demonstrated excellent signal amplification. This study reports an electrochemically reduced graphene oxide (ERGO)/mercury film (HgF) nanocomposite-modified pencil graphite electrode (PGE) prepared through successive electrochemical reduction of graphene oxide (GO) sheets and an in situ plated HgF. The ERGO-PG-HgFE, in combination with dimethylglyoxime (DMG) and square-wave adsorptive cathodic stripping voltammetry (SW-AdCSV), was evaluated for the determination of Ni²⁺ in tap and natural river water samples. A single-step electrode pre-concentration approach was employed for the in situ Hg-film electroplating, metal-chelate complex formation, and non-electrolytic adsorption at –0.7 V. The current response due to nickel-dimethylglyoxime [Ni(II)-DMG₂] complex reduction was studied as a function of experimental paratmeters including the accumulation potential, accumulation time, rotation speed, frequency and amplitude, and carefully optimized for the determination of Ni²⁺ at low concentration levels (μg?L^?1) in pH 9.4 of 0.1 M NH₃–NH₄Cl buffer. The reduction peak currents were linear with the Ni²⁺ concentration between 2 and 16?μg?L^?1. The limits of detection and quantitation were 0.120?±?0.002?µg?L^?1 and 0.401?±?0.007?µg?L^?1 respectively, for the determination of Ni²⁺ at an accumulation time of 120?s. The ERGO-PG-HgFE further demonstrated a highly selective stripping response toward Ni²⁺ determination compared to Co²⁺. The electrode was found to be sufficiently sensitive to determine metal ions in water samples at 0.1?µg?L^?1, well below the World Health Organization standards.     

Separation of Ni<Superscript>2+</Superscript> from ammonia solution through a supported liquid membrane impregnated with Acorga M5640

Separation of Ni²⁺ from ammonia/ammonium chloride solution using a flat-sheet supported liquid membrane (SLM) impregnated with Acorga M5640 in kerosene was investigated. The fundamental experimental variables influencing Ni²⁺ transport, such as ammonia concentration, carrier concentration, H₂SO₄ concentration in the stripping solution, stirring speed, and initial Ni²⁺ concentration were studied. Almost all of Ni²⁺ was transported from the feed to the stripping phase after 18 h of operation with a permeability coefficient of 9.28 × 10^?6 m s^?1 under optimum conditions: stirring speed of 1000 rpm in both phases, 20 vol.% Acorga M5640 as the carrier, 1.70 mmol L^?1 Ni²⁺ in the feed phase and 0.10 mol L^?1 H₂SO₄ in the stripping phase. The flux value of Ni²⁺ was 15.82 × 10^?6 mol m^?2 s^?1. Additionally, the influences of temperature and ultrasound on flux were examined, and results indicated that higher temperature and ultrasonic assistance improved transport of Ni²⁺ through the SLM. Selective separation of nickel from cobalt in an ammonia/ammonium chloride solution was also achieved through SLM. The stability of the SLM was examined on a continuous run mode and satisfactory stability of the nickel permeation was observed for 84 h (7 runs).     

Improved Voltammetric Response of L‐Tyrosine on Multiwalled Carbon Nanotubes‐Ionic Liquid Composite Coated Glassy Electrodes in the Presence of Cupric Ion

L ‐Tyrosine can exhibit a small anodic peak on multiwalled carbon nanotubes (MWCNTs) coated glassy carbon electrodes (GCE). At pH 5.5 its peak potential is 0.70 V (vs. SCE). When an ionic liquid (i.e., 1‐octyl‐3‐methylimidazolium hexafluorophosphate, [omim][PF₆]) is introduced on the MWCNT coat, the peak becomes bigger. Furthermore, in the presence of Cu²⁺ ion the anodic peak of L ‐tyrosine increases further due to the formation of Cu²⁺‐L ‐tyrosine complex, while the peak potential keeps unchanged. Therefore, a sensitive voltammetry based on the oxidation of Cu²⁺‐L ‐tyrosine complex on MWCNTs‐[omim][PF₆] composite coated electrode is developed for L ‐tyrosine. Under the optimized conditions, the anodic peak current is linear to L ‐tyrosine concentration in the range of 1×10^?8–5×10^?6 M, and the detection limit is 8×10^?9 M. The modified electrode shows good reproducibility and stability. In addition, the voltammetric behavior of other amino acids is explored. It is found that among them tryptophan (Trp) and histidine (His) can also produce sensitive anodic peak under same experimental conditions, and their detection limits are 4×10^?9 M and 4×10^?6 M, respectively.     

Sensing nitrite with a glassy carbon electrode modified with a three-dimensional network consisting of Ni<Subscript>7</Subscript>S<Subscript>6</Subscript> and multi-walled carbon nanotubes

We describe an amperometric sensor for nitrite that is based on a glassy carbon electrode modified with a 3-dimensional network consisting of Ni₇S₆ and multi-walled carbon nanotubes. The nickel sulfide was prepared by a hydrothermal method starting from nickel chloride and thiourea. The morphology and catalytic properties of the sensor material were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, cyclic and linear sweep voltammetry, electrochemical impedance spectroscopy, and chronoamperometry. The results showed the Ni₇S₆/MWCNTs to possess improved catalytic activity towards the oxidation of nitrite when compared to plain Ni₇S₆. The sensor is best operated at 0.425 V (vs. Ag/AgCl) in 0.1 M NaOH solution where it shows a linear response in the 1.0 μM to 4.2 mM nitrite concentration range, with a sensitivity as high as 185.0 μA·mM^?1·cm^?2 and a 0.3 μM detection limit (at a signal-to-noise ratio of 3). These features are mainly attributed to the large specific surface area of Ni₇S₆, the good electrical conductivity of the MWCNTs, and the synergy between Ni₇S₆ and the MWCNTs. The method was applied to the determination of nitrite in (spiked) water samples where it gave recoveries that ranged between 98.6 and 100.1 %.

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Graphical abstract Ni₇S₆ was synthesized by a hydrothermal method. The sensor based on Ni₇S₆/MWCNTs is best operated at 0.425 V (vs. Ag/AgCl), where it shows a linear response in the 1.0 μM - 4.2 mM nitrite concentration range, with a sensitivity as high as 185.0 μA·mM￣¹·cm￣² and a 0.3 μM detection limit. SC(NH₂)₂: thiourea; EA: ethanolamine; MWCNTs: multi-walled carbon nanotubes

     

Development of a facile sensor for the determination of Brilliant Blue FCF in beverages

A facile method was developed for the detection of Brilliant Blue FCF (BB FCF) (E133), a synthetic soluble colorant in common beverages. The method is based on a new composite of multi-walled carbon nanotube (MWCNT)-graphite oxide (GO)-room temperature ionic liquids (MWCNT/GO-RTIL) of 1-butyl-3-methylimidazolium hexafluorophosphate with high dispersibility and strong conductivity. Differential pulse stripping voltammetry (DPSV) and the MWCNT/GO-RTIL composite-modified glassy carbon electrode (GCE) were used to determine the BB FCF in this work. Under the optimum experimental conditions, the oxidation current of BB FCF was proportional to its concentration in two linear ranges, from 6.34 μg kg^?1 to 7.93 × 10² μg kg^?1 and 7.93 × 10² μg kg^?1 to 7.93 × 10³ μg kg^?1.

The detection limit was down to 3.01 μg kg^?1 at signal-to-noise ratio of 3. Also, this method has been successfully applied in the determination of BB FCF in common beverage samples, including RIO cocktail, Bacardi Breezer and Reinnbow rum dinks. The assay results of BB FCF in drink samples obtained by the proposed method were in a good agreement with the reference values detected by high performance liquid chromatography (HPLC). The proposed method provided a useful tool for the assay of BB FCF in drink samples.     

Fabrication of a nanostructured TiO2/carbon nanotube composite electrode for voltammetric and impedimetric determination of NTO explosive in the water and soil samples

An electrochemical oxidation route was developed for sensitive and selective assay of nitrotriazolone (NTO) explosive in some environmental samples on a multi-walled carbon nanotube (MWCNTs)/TiO₂ nanocomposite paste electrode, for prevention of the analytical interference of conventional reducible energetic compounds. Detailed evaluations were made for the electrochemical behaviour of NTO on the modified electrode by adsorptive stripping voltammetry, electrochemical impedance spectroscopy (EIS) and chronoamperometry techniques in the pH range of 2.0–10.0. Parameters such as diffusion coefficient constant of NTO were calculated, and various experimental conditions were also optimised. Under optimal conditions the calibration curve had two linear dynamic ranges of 130.0–3251.5 μg L^?1 and 6.5–26.0 mg L^?1 with a detection limit of 26.0 μg L^?1 (0.2 μmol L^?1) and precision of <3%. This electrochemical sensor was further applied to determine NTO in real soil and water samples with satisfactory results.     

New Ni(II) Ion-Selective Electrode Based on the N-S Schiff Base Ligand as Neutral Carrier in PVC Matrix

Abstract

A nickel(II) [Ni(II)] ion-selective electrode was prepared by incorporating a new N-S Schiff base ligand, glyoxal-bis(S-benzyldithiocarbazate) (GBSB), as a neutral carrier into the PVC matrix. The proposed electrode exhibits an excellent near-Nernstian response for Ni²⁺ ions, ranging from 2.8 × 10^?7 to 1.0 × 10^?1 mol/L with a detection limit of 1.2 × 10^?7 mol/L and a slope of 31.9 ± 0.3 mV/dec in pH 4.0 nitrate buffer solution at 25°C. It has an appropriate response time and suitable reproducibility and can be used for at least 3 months. The operational pH range of the proposed electrode is 4.0–7.5. The response mechanism is discussed in view of the alternating current (AC) impedance technique. In addition, the electrode was successfully used as an indicator electrode in potentiometric titration of Ni²⁺ ion and in the direct determination of Ni²⁺ ion in milk power and chocolate samples.     

Electrocatalytic oxidation of methanol by ZSM-5 nanozeolite-modified carbon paste electrode in alkaline medium

Development of a novel modified electrode for electrocatalytic oxidation of methanol in order to decrease overvoltage is importance. In this paper, carbon paste electrode (CPE) was modified by ZSM-5 nanozeolite. The average diameter of used nanozeolite was 97 nm. Ni²⁺ ions were incorporated to the nanozeolite by immersion of the modified electrode in a 0.1 M nickel chloride solution. Then, electrochemical studies of this electrode were performed by using cyclic voltammetry(CV) in alkaline medium. This modified electrode was used as an anode for the electrocatalytic oxidation of methanol in 0.1 M of NaOH solution. The obtained data demonstrated that ZSM-5 nanozeolite at the surface of CPE improves catalytic efficiency of the dispersed nickel ions toward methanol oxidation. The values of electron transfer coefficient, charge-transfer rate constant, and the electrode surface coverage are obtained 0.61, 0.2342 s^?1, and 4.33 × 10^?8 mol cm^?2, respectively. Also, the mean value of catalytic rate constant between the methanol and redox sites of electrode and diffusion coefficient were found to be 2.54 × 10⁴ cm³ mol^?1 s^?1 and 1.85 × 10^?8 cm² s^?1, respectively. Obtained results from both CV and chronoamperometric techniques indicated that the electrode reaction is a diffusion-controlled process.     

Optimized solid phase extraction based on diethyldithiocarbamate-coated Fe3O4 magnetic nanoparticles followed by ICP-OES for determination of Cd(II) and Ni(II) in rice and water samples

In the present study, application of Fe₃O₄ magnetic nanoparticles (MNPs) coated with diethyldithiocarbamate as a solid-phase sorbent for extraction of trace amounts of cadmium (Cd²⁺) and nickel (Ni²⁺) ions by the aid of ultrasound was investigated. The analytes were determined by inductively coupled plasma-optical emission spectroscopy. Fe₃O₄ MNPs were prepared by solvothermal method and characterized with dynamic light scattering, scanning electron microscope and X-ray diffraction. Response surface methodology was used for optimization of the extraction process and modeling the data. The optimal conditions obtained were as follows: chelating agent, 1.2 g L^?1; pH, 6.13; sonication time, 13 min and Fe₃O₄ MNPs, 10.3 mg. The calibration curves were linear over the concentration range of 1–1,000 μg L^?1 for Cd²⁺ and 2.5–1,000 for Ni²⁺ with the determination coefficients (R ²) of 0.9997 and 0.9995, respectively. The limits of detection were 0.27 μg L^?1 for Cd²⁺ and 0.76 μg L^?1 for Ni²⁺. The relative standard deviations (n = 7, C = 200 μg L^?1) for determination of Cd²⁺ and Ni²⁺ were 2.0 and 2.7 %, respectively. The relative recoveries of the analytes from tap, river and lagoon waters and rice samples at the spiking level of 10 μg L^?1 were obtained in the range of 95–105 %.     

Evaluation of the Potentialities of a Carbon Nanotubes/Silicone Rubber Composite Electrode in the Determination of Hydrochlorothiazide

A multiwall carbon nanotube/silicone rubber (MWCNT/SR) composite electrode has been used for the determination of hydrochlorothiazide (HCTZ) in pharmaceutical formulations by differential pulse voltammetry (DPV). The electro-oxidation process was evaluated by cyclic voltammetry, from which it was observed that HCTZ presents an irreversible oxidation peak at 0.82 V vs. saturated calomel electrode (SCE) in the potential range from 0.5 to 1.1 V, in Britton-Robinson buffer pH 7.0 at MWCNT/SR. HCTZ was determined by DPV using a MWCNT/SR 70% (MWCNT, m/m) composite electrode after the optimization of the experimental parameters. The linear range was from 5.0 to 70.0 µ mol L^?1, with a limit of detection (LOD) of 2.6 µ mol L^?1. The HCTZ was determined in pharmaceutical formulations using the proposed composite electrode and the results agreed with those from the official high performance liquid chromatography (HPLC) method within 95% confidence level, according to the t-Student test.     

Synthesis and characterisation of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) Zr(IV) monothiophosphate composite cation exchanger: analytical application as lead ion selective membrane electrode

A Pb²⁺ ion selective membrane electrode based on poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) Zr(IV) monothiophosphate composite cation exchange material was fabricated using solution casting method. The effect of membrane composition on the proton exchange capacity was investigated by using varying amounts of electroactive material. The membrane with 250 mg of electroactive material and 10 µL of plasticiser exhibited higher proton conductivity. The optimised membrane composition was used for the fabrication of ion selective membrane electrode which exhibited typical Nernstian response towards Pb²⁺ ions in the concentration range 20.70 gL^?1–20.7 µgL^?1 (1 × 10^–1–1 × 10^–7 mol L^?1) with a sub-Nernstian slope of 27.429 mV per decade change in Pb²⁺ ion concentration. The response time of the electrode under study for Pb²⁺ ions was found to be 11 s and the electrode can be used for 120 days without any considerable divergence in response potential. It can also be successfully used in the pH range from 3.0 to 6.5. It was found selective for Pb²⁺ ions in the presence of various monovalent, divalent and trivalent interfering metal ions. It was also employed as an indicator electrode in the potentiometric titration of Pb²⁺ ions using ethylenediaminetetraacetic acid, disodium salt, as a titrant.     

Synthesis of metal (Fe or Pd)/alloy (Fe–Pd)‐nanoparticles‐embedded multiwall carbon nanotube/sulfonated polyaniline composites by γ irradiation

Composites of multiwall carbon nanotubes (MWCNTs) and sulfonated polyaniline (SPAN) were prepared through the oxidative polymerization of a mixture of aniline, 2,5‐diaminobenzene sulfonic acid, and MWCNTs. Fe, Pd, or Fe–Pd alloy nanoparticles were embedded into the MWCNT–SPAN matrix by the reduction of Fe, Pd, or a mixture of Fe and Pd ions with γ radiation. Sulfonic acid groups and the emeraldine form of backbone units in SPAN served as the source for the reduction of the metal ions in the presence of γ radiation. The existence of metallic/alloy particles in the MWCNT–SPAN matrix was further ascertained through characterization by high‐resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, thermogravimetric analysis, and conductivity measurements. HRTEM pictures clearly revealed the existence of Fe, Pd, and Fe–Pd nanoparticles of various sizes in the MWCNT–SPAN matrices. There were changes in the electronic properties of the MWCNT–SPAN–M composites due to the interaction between the metal nanoparticles and MWCNT–SPAN. Metal‐nanoparticle‐loaded MWCNT–SPAN composites (MWCNT–SPAN–M; M = Fe, Pd, or Fe–Pd alloy) showed better thermal stability than the pristine polymers. The conductivity of the MWCNT–SPAN–M composites was approximately 1.5 S cm^?1, which was much higher than that of SPAN (2.46 × 10^?4 S cm^?1). Metal/alloy‐nanoparticle‐embedded, MWCNT‐based composite materials are expected to find applications in molecular electronics and other fields. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3355–3364, 2006     

Sensitive electrochemical DNA-based biosensors for the determination of Ag<Superscript>+</Superscript> and Hg<Superscript>2+</Superscript> ions and their application in analysis of amalgam filling

In the present paper, we used single-stranded poly-T (100% thymine bases) and poly-C (100% cytosine bases) nucleic acids as DNA probes for selective and sensitive individual electrochemical determination of Hg²⁺ and Ag⁺_, respectively, on the multi-walled carbon nanotube paste electrodes (MWCNTPEs) using [Fe(CN)₆]^3?/4? as electroactive labels. In the presence of Hg²⁺ and Ag⁺, the probe–Hg²⁺/Ag⁺ interactions through T–Hg²⁺–T and C–Ag⁺–C complexes formation could cause the formation of a unimolecular hybridized probe. This structure of probe led to its partial depletion from electrode surface and facilitation of electron transfer between [Fe(CN)₆]^3?/4? redox couple and electrode surface, resulting in the enhanced differential pulse voltammetry (DPV) oxidation current of [Fe(CN)₆]^3?/4? at the probe-modified electrode surface. We applied the difference in the oxidation peak currents of [Fe(CN)₆]^3?/4? before and after Hg²⁺/Ag⁺–DNA probe bonding (?I) for electrochemical determination of these heavy metal ions. Detection limits were 8.0?×?10^?12 M and 1.0?×?10^?11 M for Hg²⁺ and Ag⁺ ions determination, respectively. The biosensors were utilized to determine the weight percent of toxic metals, i.e., silver and mercury in dental amalgam filling composition. The results of their practical applicability in analysis of the amalgam sample were satisfactory.     

A highly sensitive sensor of paracetamol based on zinc-layered hydroxide-<Emphasis Type="Italic">L</Emphasis>-phenylalanate-modified multiwalled carbon nanotube paste electrode

A new zinc-layered hydroxide-L-phenylalanate (ZLH-LP)-modified multiwalled carbon nanotube (MWCNT) was prepared as a new material of paste electrode for the detection of paracetamol (PCM) in 1.0?×?10^?1 M phosphate buffer solution and at pH 7.5. The electrochemical characterization of the MWCNTs/ZLH-LP paste electrode was characterized by square wave voltammetry, electrochemical impedance spectroscopy, and cyclic voltammetry while the morphology properties of the MWCNTs, ZLH-LP, and MWCNTs/ZLH-LP were investigated using transmission electron microscopy and scanning electron microscopy. Under optimized conditions, the MWCNTs/ZLH-LP paste electrode demonstrated an excellent electrocatalytic activity towards oxidation of PCM in the linear responses’ ranges from 7.0?×?10^?7 M to 1.0?×?10^?4 M (correlation coefficient, 0.996) with the limit of detection obtained at 8.3?×?10^?8 M. As a conclusion, the MWCNTs/ZLH-LP paste electrode revealed good repeatability, reproducibility, and stability, and was found to be applicable for use in pharmaceutical tablet samples.

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Graphical abstract ?

     

Novel 1,8-naphthalimide dye for multichannel sensing of H<Superscript>+</Superscript> and Cu<Superscript>2+</Superscript>

A novel 1,8-naphthalimide dye with simple structure has been produced by a facile synthetic method for colorimetric and fluorescent sensing of H⁺ and Cu²⁺. In CH₃CN/H₂O (1/1, v/v), the dye could monitor H⁺ using dual channels (ratiometric absorbance and fluorescence intensity change) from pH 6.2 to 12.0. Meanwhile, in the pH range of 1.9–5.2, the dye could also be used to detect Cu²⁺ using triple channels [ultraviolet–visible (UV–Vis) absorption, fluorescence intensity reduction, as well as fluorescence blueshift]. The detection limits for Cu²⁺ evaluated by colorimetric and fluorescent titration were 6.10 × 10^?7 and 2.62 × 10^?7 M, respectively. The dye exhibited specific selectivity and sensitivity for H⁺ and Cu²⁺ over various coexisting metal ions. Moreover, the sensing mechanism of the dye for H⁺ and Cu²⁺ was carefully examined.     

A new Schiff base fluorescent indicator for the detection of Mg<Superscript>2+</Superscript> and its application to real samples

A new Schiff base fluorescence probe, 3-Allylsalicylaldehyde salicylhydrazone (L), for Mg²⁺ was designed and synthesized. The fluorescence of the sensor L was enhanced remarkably by Mg²⁺ with 2:1 binding ratio, and the binding constant was determined to be 1.02 × 10⁷ M^?1. Probe L had high sensitivity for Mg²⁺ in a solution of DMF/water (4:1, v/v, pH 7.5), and the detection limit was 4.88 × 10^?8 mol/L. Common coexistent metal ions, such as K⁺, Na⁺, Ag⁺, Ca²⁺, Zn²⁺, Ba²⁺, Bi²⁺, Cu²⁺, Ni²⁺, Hg²⁺, Fe³⁺ , and Al³⁺, showed little or no interference on the detection of Mg²⁺ in solution. The fluorescence probe L, which was successfully used for the determination of trace Mg(II) in real samples, was shown to be promising for liquid-phase extraction coupled with fluorescence spectra.     

A new calix[4]arene Schiff base sensor for Hg<Superscript>2+</Superscript> and Au<Superscript>3+</Superscript>

This article reports the selective sensing ability of a newly synthesized calix[4]arene Schiff base (C4TSB) derivative. C4TSB exhibited strong turn-off fluorescence affinity for Hg²⁺ and Au³⁺. The selective sensing ability of receptor was investigated in the presence of different co-existing competing ions. The limit of detection for Hg²⁺ and Au³⁺ was determined as 1.9 × 10^?5 and 1.0 × 10^?6 M, respectively. Receptor forms 1:1 stoichiometric complex with both metals and their binding constants were calculated as 7.9 × 10³ M^?1 for Hg²⁺ and 5.7 × 10³ M^?1 for Au³⁺. Complexes were also characterized through FT-IR spectroscopy.