Anthroneamine based chromofluorogenic probes for Hg2+ detection in aqueous solution

Anthroneamine derivatives 1–3 (H₂O:DMSO; 9:1, HEPES buffer, pH 7.0 ± 0.1) undergo highly selective fluorescence quenching with Hg²⁺. The observed linear fluorescence intensity change allows the quantitative detection of Hg²⁺ between 200 nM/40 ppb—12 μM/2.4 ppm even in the presence of interfering metal ions viz. Na⁺, K⁺, Mg²⁺, Ca²⁺, Ba²⁺, Cr³⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Ag⁺, Cd²⁺, Pb²⁺. Probes 1–3 and their Hg²⁺ complexes also show the broad pH resistance for their practical applicability.     

Analytical characteristics of a high efficiency ion transmission interface (S mode) inductively coupled plasma mass spectrometer for trace element determinations in geological and environmental materials

The analytical performance of a high transmission interface (S mode), inductively coupled plasma-quadrupole mass spectrometer (the VGE Plasma Quad 3) was evaluated for multitrace element analysis of geological and environmental materials. The sensitivity, limits of detection (LODs), effect of Ca and Na and other major elements on mass response, background, percentage ¹⁵⁶CeO⁺/¹⁴⁰Ce⁺, ⁷⁰Ce⁺⁺/¹⁴⁰Ce⁺, and long- and short-term variations were compared with those obtained with the conventional mode (normal mode). Normal mode sensitivities varied from 20 MCPS ppm⁻¹ (millions of counts per second per ppm) for ⁹Be⁺, 70–80 MCPS ppm⁻¹ for ⁵⁹Co⁺, 90 for ¹¹⁵In⁺ and 40–50 MCPS ppm⁻¹ for the heavy masses. S mode sensitivities were 180 MCPS ppm⁻¹ for ⁵⁹Co⁺, 350–380 for ¹¹⁵In⁺ and ¹⁴⁰Ce⁺, 300 MCPS ppm⁻¹ for ²⁰⁸Pb⁺, and 150 MCPS ppm⁻¹ for ²³²Th⁺ and ²³⁸U⁺, i.e. enhancements amounting to 7. Three σ normal and S mode LODs are mainly in the 1–2 and 0.1 ppt range, respectively. S mode LODs are enhanced relative to the normal mode, for masses >80 amu, by factors ranging from about 10 to 50. S mode LODs are depressed relative to normal mode LODs for masses <50 amu by a factor of 10, and the extent of depression is related linearly to mass. In the high- and mid-mass ranges, backgrounds were about 10. They were not affected by sample composition: at 8 amu the S mode background for real samples amounted to about 20, whereas at 220 amu it amounted to four counts. S and normal mode percentage ¹⁵⁶CeO⁺/¹⁴⁰Ce⁺⁺ and percentage Ce⁺⁺/Ce⁺ ratios were about 1.5%, and temporal variations were insignificant. The percentage RSDs of normal and S mode Sr⁺, Ag⁺ and Pb⁺ isotope ratios were about 0.1%, with the exception of S mode ²⁰⁸Pb⁺ and ²⁰⁸Pb⁺/²⁰⁶Pb⁺ ratios in the presence of NaCl, which were degraded by a factor of about 2. Normal and S mode long-term variations for continuous aspiration of 0.1% NaCl for periods of up to 13 h were mass dependent, varying from 2.5–4% for ⁷Li⁺ and ⁹Be⁺ to about 2% for the mid-mass range, increasing slightly to about 3% for high masses. Most of this variation occurred during the first 100–150 min of the analysis during cone priming. With compensation, normal and S mode long-term percentage RSDs and drift were reduced to 1–2%. These variations indicate that extended periods of S mode analysis can be conducted without periodic recalibration. A calibration procedure, based on spiked HNO₃, was validated by analysing spiked NaCl solutions, standard water and geological standard reference material (SRM) solutions with internal standardization using conventional solution delivery and flow injection. The agreement of the S mode data and the certified and literature values for ultratrace elements, including ppt levels of rare earth elements in the water standards, was satisfactory. An important conclusion is that ion sampling effects in the S mode are minimal and that the enhanced ion transmission interface is not only beneficial for microanalysis using laser ablation, but for geological and environmental type solutions as well. Sensitivity enhancements were preserved and matrix effects were approximately ±20% for solutions containing 0.1–0.2% total dissolved salt concentration. These variations were reduced to <5% with internal standards matched in mass and ionization potential.     

Electrochemical deposition of PbTe onto n-Si(1 0 0) wafers

Electrochemical deposition of PbTe from 50 mM Pb(NO₃)₂ + 1 mM TeO₂ + 0.1 M HNO₃ solution onto n-Si(1 0 0) wafers was studied using cyclic voltammetry (CV), chronoamperometry, ex situ SEM, XRD and EDX. Electrochemical behavior of n-Si(1 0 0) electrode in electrolytes 50 mM Pb(NO₃)₂ + 0.1 M HNO₃ and 1 mM TeO₂ + 0.1 M HNO₃ was also studied. No underpotential deposition (UPD) of Pb and Te onto n-Si was observed in the investigated systems indicating weak Pb–Si and Te–Si interactions. Deposition of Pb and Te on n-Si occurred with overvoltage via 3D island growth. Electrosynthesis of PbTe (NaCl-like structure, a = 0.650 nm) takes place due to codeposition of Pb and Te at potentials E > E_{Pb²⁺/Pb⁰} (lead UPD onto tellurium). Cathodic deposition of PbTe onto n-Si(1 0 0) is irreversible – there is no anodic current in the CV curve. Oxidation of PbTe on n-Si is observed only under illumination, when photoelectrons and photoholes are generated in silicon substrate.     

Carbon nanofiber electrode array for the detection of lead

A nanoelectrode array of vertically aligned carbon nanofibers was evaluated for the detection of Pb^2 + by anodic stripping voltammetry. The achieved detection limit of 1.73 nM is well below the environmental guidelines. The approach provides a safer alternative to the mercury electrodes commonly used for the detection of heavy metals.     

Measurement and modelling of mean activity coefficients of aqueous mixed electrolyte solution containing glycine

Electrochemical measurements were made on (H₂O + NaBr + K₃PO₄ + glycine) mixtures at T = 298.15 K by using ion selective electrodes. The mean ionic activity coefficients of NaBr at molality 0.1 were determined at five K₃PO₄ molalities (0.01, 0.03, 0.05, 0.07, and 0.1) mol · kg⁻¹. The activity coefficients of glycine were evaluated from mean ionic activity coefficients of NaBr. The modified Pitzer equation was used to model the experimental data.     

Temperature controlled ionic liquid-dispersive liquid phase microextraction for determination of trace lead level in blood samples prior to analysis by flame atomic absorption spectrometry with multivariate optimization

This paper described a new approach for the preconcentration of lead (Pb²⁺) by temperature controlled ionic liquid-dispersive liquid phase microextraction (TIL-DLME) prior to analyzing by flame atomic absorption spectrometry (FAAS). An ionic liquid (IL) 1-Butyl-3-methylimidazolium hexafluorophosphate [C₄MIM][PF₆] was used as an extractant solvent. The Pb²⁺ was complexed with ammonium pyrrolidinedithiocarbamate (APDC) and then entered into the infinite IL drops at high temperature (> 70 °C). Important variables affecting the microextraction efficiency such as pH, ligand concentration, amount of IL, temperature and incubation time were investigated. The results showed that the coexistent ions had no obvious negative effect on the determination of Pb²⁺. In the optimum experimental conditions, the limit of detection (LOD) and the enhancement factor (EF) were 0.13 μg L^? 1 and 93, respectively. The relative standard deviation (RSD) of 10 μg L^? 1 Pb²⁺ was 4.3%. The developed method was validated by determining Pb²⁺ in certified reference material (CRM) and the results showed that the determined values of Pb²⁺ were in good agreement with the certified value. The proposed method was applied satisfactorily for the preconcentration of Pb²⁺ in acid digested blood samples of children with different respiratory disorders.     

Zeptomolar detection of Hg2 + based on label-free electrochemical aptasensor: One step closer to the dream of single atom detection

An ultra-sensitive and highly selective electrochemical label-free aptasensor is proposed for the quantitation of Hg^2 + based on the hybridization/dehybridization of double-stranded DNA (dsDNA) on a gold electrode. Thiol-substituted single-stranded DNA (ssDNA) is self-assembled on the gold electrode surface through the SAu interaction. The hybridization of ssDNA with complementary DNA (cDNA) and the consequences of dehybridization in the presence of mercury ions are followed through differential pulse voltammetry (DPV) responses using a [Fe(CN)₆]^{3 −/4 −} redox probe. The formation of a thymine–Hg^2 +–thymine (T–Hg^2 +–T) complex is the key to producing a highly selective and sensitive aptasensor for Hg^2 + determination. Specifically, the present electrochemical aptasensor is able to quantify Hg^2 + ions in concentrations from 5 zeptomolar (zM) to 55 picomolar (pM) with a limit of detection of 0.6 zM, close to the dream of single atom detection, without requiring a complicated procedure or expensive materials.     

A study of the photodeposition over Ti/TiO2 electrode for electrochemical detection of heavy metal ions

Here we reported that UV light irradiation can significantly enhance sensitivity of Ti/TiO₂ electrode for determination of trace heavy metal ions (such as Cu^2 +, Pb^2 + and Cd^2 +) owing to the photodeposition of metal ions on the surface of electrodes. The sensitivity of heavy metal ions can be selectively enhanced over the Ti/TiO₂ electrode, which is attributed to matching between potential of heavy metal ions and the position of the conduction band of TiO₂.     

Voltammetric study on the mechanism of ion transfer caused by weak acids in the bilayer lipid membrane

The mechanism has been investigated by cyclic voltammetry for the ion transfer from one aqueous phase (W1) to another (W2) across a bilayer lipid membrane (BLM) in the presence of a typical uncoupler, carbonylcyanide p-trifluoromethoxyphenylhydrazone (FCCP). Voltammograms for the ion transfer were in steady-state and showed rotated sigmoidal and symmetrical shape about the origin (0 V, 0 A). The magnitude of the ion transfer current at a given applied potential increased linearly with the concentration of FCCP in W2 up to 10⁻⁶ M and then became saturated. The ion transfer current also showed a bell-type dependence on pH centered around pH ≅ pK_a + 1, K_a being the dissociation constant of FCCP in aqueous phase. These properties have been well explained by our proposed model that the ion transfer current is attributable to the transfers of H⁺ and Na⁺ distributed in BLM. The hydrophilic counter ions, H⁺ and Na⁺, compensate the negative charge of the dissociated FCCP in BLM. The current intensity is predominantly governed by the concentration and the ion mobility of the counter cations.     

Facile one-pot synthesis of fluorinated graphene oxide for electrochemical sensing of heavy metal ions

Doping and functionalization could significantly assist in the improvement of the electrochemical properties of graphene derivatives. Herein, we report a one-pot synthesis of fluorinated graphene oxide (FGO) from graphite. The surface morphology, functionalities and composition of the resulting FGO have been studied using various surface characterization techniques, revealing that layer-structured nanosheets with ~ 1.0 at.% F were formed. The carbon bound F exhibited semi-ionic bonding characteristic and significantly increased the capacitance of FGO compared to GO. Further, the FGO has been employed for the simultaneous detection of heavy metal ions Cd^2 +, Pb^2 +, Cu^2 + and Hg^2 + using square wave anodic stripping voltammetry; and a substantial improvement in the electrochemical sensing performance is achieved in comparison with GO.     

Thermodynamics of the O2/O2− redox couple in molten (LiCl + KCl + Li2O) systems

Activity coefficients of oxide ion were determined by the measurements of the standard formal potential of O₂/O^2? with a boron-doped diamond (BDD) electrode in molten (LiCl + KCl): LiCl:KCl = {58.5:41.5 (eutectic), 65:35, 70:30, 75:25} mol% at T = (673 to 803) K. The activity coefficient decreases with the increase of the LiCl content in the melt: (18.7 ± 1.5, 7.7 ± 1.0, 4.1 ± 0.4, and 1.6 ± 0.1), respectively, at T = 773 K in each melt. The result is explained by the attractive force between Li⁺ and O^2? which is stronger than that between K⁺ and O^2?.     

The Use of Stripping Voltammetry for Lead Determination during Toxic Chemicals Detoxication by an Electrochemical Method

The paper describes the results of stripping voltammetry usage to control concentration of lead ion which are formed during electrochemical detoxication of organic pollutants. Optimal conditions for the analysis of Pb²⁺ were selected, i.e. 0.05 N KOH is an electrolyte, the deposition potential (-0.55) V, deposition time of 4 minutes, the amount of analyzed sample was 0.1 ml. The presence of organic matter does not affect the quantitative determination of lead ions. The developed method allows us to estimate the concentration of Pb²⁺ in the amount of electrolyte at disposal of toxicants quickly and with a high degree of sensitivity.     

Determination of inorganic and total mercury by vapor generation atomic absorption spectrometry using different temperatures of the measurement cell

A simple and inexpensive laboratory-built flow injection vapor generation system coupled to atomic absorption spectrometry (FI-VG AAS) for inorganic and total mercury determination has been developed. It is based on the vapor generation of total mercury and a selective detection of Hg^2 + or total mercury by varying the temperature of the measurement cell. Only the inorganic mercury is measured when the quartz cell is at room temperature, and when the cell is heated to 650 °C or higher the total Hg concentration is measured. The organic Hg concentration in the sample is calculated from the difference between the total Hg and Hg^2 + concentrations. Parameters such as the type of acid (HCl or HNO₃) and its concentration, reductant (NaBH₄) concentration, carrier solution (HCl) flow rate, carrier gas flow rate, sample volume and quartz cell temperature, which influence FI-VG AAS system performance, were systematically investigated. The optimized conditions for Hg^2 + and total Hg determinations were: 1.0 mol l^− 1 HCl as carrier solution, carrier flow rate of 3.5 ml min^− 1, 0.1% (m/v) NaBH₄, reductant flow rate of 1.0 ml min^− 1 and carrier gas flow rate of 200 ml min^− 1. The relative standard deviation (RSD) is lower than 5.0% for a 1.0 μg l^− 1 Hg solution and the limit of quantification (LOQ, 10 s) is 55 ng g^− 1. Certified samples of dogfish muscle (DORM-1 and DORM-2) and non-certified fish samples were analyzed, using a 6.0 mol l^− 1 HCl solution for analyte extraction. The Hg^2 + and CH₃Hg⁺ concentrations found were in agreement with certified ones.     

Operando soft x-ray emission spectroscopy of LiMn2O4 thin film involving Li–ion extraction/insertion reaction

We developed an electrochemical in situ cell for soft x-ray emission spectroscopy (XES) to accurately investigate the redox reaction and electronic structure of transition metals in the cathode materials for Li–ion battery. The in situ cell consists of a Li–metal counter electrode, an organic electrolyte solution, and a cathode on a membrane window which separates the liquid electrolyte from high vacuum and can pass the incoming and emitted photons. In this study, the Mn 3d electronic structure of LiMn₂O₄ thin-film electrode was clarified by the operando XES. At the charged state, the XES spectrum changed significantly from the open-circuit-voltage (OCV) state, suggesting oxidation of the Mn^3 + component through Li–ion extraction. Upon discharge up to 3.0 V vs. Li/Li⁺, the XES spectrum almost returned to its profile at the OCV state with small difference, indicating the valence change of Mn: Mn^3.6 + → Mn^4 + → Mn^3.3 + corresponding to the OCV, charged, and discharged states.     

Mean activity coefficient measurement and thermodynamic modelling of the ternary mixed electrolyte (MgCl2 + glucose + water) system at T = 298.15 K

In this work, the mean activity coefficients of MgCl₂ in pure water and (glucose + water) mixture solvent were determined using a galvanic cell without liquid junction potential of type: (Mg²⁺ + ISE)|MgCl₂ (m), glucose (wt.%), H₂O (100 wt.%)|AgCl|Ag. The measurements were performed at T = 298.15 K. Total ionic strengths were from (0.0010 to 6.0000) mol · kg⁻¹. The various (glucose + water) mixed solvents contained (0, 10, 20, 30 and 40)% mass fractions percentage of glucose respectively. The mean activity coefficients measured were correlated with Pitzer ion interaction model and the Pitzer adjustable parameters were determined. Then these parameters were used to calculate the thermodynamics properties for under investigated system. The results showed that Pitzer ion interaction model can satisfactory describe the investigated system. The modified three-characteristic-parameter correlation (TCPC) model was applied to correlate the experimental activity coefficient data for under investigation electrolyte system, too.     

Conductometric study of some alkali metal halides in (dimethyl sulfoxide + acetonitrile) at T = 298.15 K

Electrolytic conductivities of some alkali metal halides, MX (M⁺ = Li⁺, Na⁺, and K⁺; X^? = Cl^?, Br^?, and I^?), NaBPh₄ and Bu₄NBr have been investigated in (20, 40, and 60) mass% {dimethyl sulfoxide (DMSO) in DMSO + acetonitrile} at T = 298.15 K. The conductance results have been analyzed by the Fuoss-conductance-concentration equation in terms of the limiting molar conductance Λ° the association constant K_A and the association diameter R. The ionic contributions to the limiting molar conductance have been estimated using Bu₄NBPh₄ as the “reference electrolyte”. The association constant K_A tends to increase in the order mass percent 20 < 40 < 60 DMSO in (DMSO + acetonitrile) which is explained by the thermodynamic parameter ΔG° and Walden product Λ°η. The results have been interpreted in terms of ion–solvent interactions and structural changes in the mixed solvents.     

Measurement of the local temperature in an ion track using low-dimensional quantum confinement structure

We measured the local temperature in an ion track utilizing fast exciton recombination in (C₃H₇NH₃)₂PbBr₄. We obtained the local temperatures of 1000–1500 K for 1.0 MeV H⁺, 2.0 MeV H⁺ and He⁺, and the local temperature was found to be an increasing function of the linear energy transfer. Furthermore, the measured local temperature increased with increasing ion dose, which is attributed to the diffusion of the phonons in an ion track.     

Mean activity coefficients of NaCl in (sodium chloride + sodium bicarbonate + water) fromT = (293.15 to 308.15) K

The mean activity coefficients of NaCl in (sodium chloride  +  sodium bicarbonate  +  water) were determined experimentally in the temperature range 293.15 K to 308.15 K at four NaHCO₃molality fractions (0.1, 0.3, 0.5, and 0.7). The measurements were made with an electrochemical cell, using a Na ⁺ glass ion-selective electrode and a Cl ⁻ solid-state ion-selective electrode. The experimental values reported by Butler and Huston are found to be higher than those calculated from the Pitzer equation using the existing parameters while the experimental results of this work are close to the calculated values, up to an NaHCO₃molality fraction of 0.5. At the NaHCO₃molality fraction of 0.7, the experimental data are much lower than the calculated values, implying that the interference of HCO₃ ⁻ on the Na ⁺ glass ion-selective electrode can only be neglected up to a molality fraction of NaHCO₃of 0.5, an observation which is consistent with that of Butler and Huston.     

Hydrothermal processing and characterization of Ce1−xPbxO2−δ solid solutions

Nanocrystals of Ce_1?xPb_xO_2?δ (x = 0.00, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, and 0.35) were prepared by a hydrothermal reaction route. During the formation reaction, buffer solutions were explored as an effective additive to retain the initial molar ratio. With increasing the Pb²⁺ content, the average crystallite size was slightly retarded. Morphologies observed by transmission electron microscope indicated that the particles were spherical-like and highly uniformed. Pb²⁺ ions are homogenously distributed in the solid solutions. Analyses using X-ray diffraction, Raman and UV spectroscopies showed that the solid solubility limit of Pb²⁺ in CeO₂ was about x = 0.20. For x < 0.20, with increasing the Pb²⁺ content, the bulk conductivity increased, and the oxygen storage capacity was enhanced as followed by a decrease in reduction temperature.     

Determination of trace amounts of cadmium by modified graphite furnace atomic absorption spectrometry after liquid phase microextraction

A simple and powerful microextraction technique was used for determination of cadmium in water samples using liquid phase microextraction (LPME) followed by graphite furnace atomic absorption spectrometry (GF-AAS). In a preconcentration step, cadmium was extracted from a 2 mL of its aqueous sample in the pH = 6 as cadmium-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) cationic complex into a 4 µL drop of nitrobenzene and ammonium tetraphenylborate as counter ion. In the drop, the cadmium-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) ammonium tetraphenylborate ion associated complex was formed. After extraction, the microdrop was retracted and directly transferred into a graphite tube modified by [Pd_(c) + Pd_(i)]. Some effective parameters on extraction and complex formation, such as type and volume of organic solvent, pH, concentration of chelating agent and counter ion, extraction time and stirring rate were optimized. Under the optimum conditions, the enrichment factor and recovery were 390 and 78%, respectively. The calibration graph was linear in the range of 0.01–1 µg L^− 1 with correlation coefficient of 0.9952 under the optimum conditions of the recommended procedure. The detection limit based on the 3Sb criterion was 0.0065 µg L^− 1 and relative standard deviation (RSD) for eight replicate measurements of 0.1 µg L^− 1 and 0.4 µg L^− 1 cadmium was 6.4 and 5.8% respectively. The characteristic concentration was 0.0014 µg L^− 1 equivalent to a characteristic mass of 5.6 fg. In order to evaluate the accuracy and recovery of the presented method the procedure was applied to the analysis of reference materials and seawater.