Electrochemical determination of lead and lead ion transfer at liquid-liquid interfaces

The transfer behavior of lead (II) ion at a liquid-liquid interface, facilitated by neutral carriers (polyethylene glycols), is studied by an electrochemical method. The transfer process is discussed in terms of the formation of complexes in two phases and attributed to the transfer of a complex ion across the interface. The apparent standard transfer potential, ΔwoφPbL2+o, apparent standard Gibbs energy of transfer, ΔwoGPbL2+o, and the dissociation constant of the complex, KPbL2+, in the aqueous phase are obtained from the experimental data. The results suggest a new electrochemical method for the determination of lead.     

Simultaneous determination of copper and lead by graphite-furnace atomic absorption spectrometry after liquid-liquid extraction of the ion pair with zephiramine

A procedure for the simultaneous determination of copper and lead by graphite-furnace atomic absorption spectrometry was investigated by means of a two-channel atomic absorption spectrometer. Both copper(II) and lead(II) are converted into their iodo complex anions and extracted quantitatively into diisobutyl ketone as their ion pairs with tetradecyldimethylbenzylammonium (zephiramine) in a 10-ml centrifuge tube. An aliquot of the organic extract is directly pipetted from the upper layer in the centrifuge tube and injected into the graphite furnace. The detection limits (S/N = 3) are 2.6 ng ml^?1 of copper and 1.0 ng ml^?1 of lead. The relative standard deviations for 10 replicate determinations are 2.9% for 20 ng ml^?1 of copper and 2.7% for 10 ng ml^?1 of lead. Results of analyses of some practical samples are given.     

A signal-on electrogenerated chemiluminescent biosensor for lead ion based on DNAzyme

A highly reproducible and sensitive signal-on electrogenerated chemiluminescence (ECL) biosensor based on the DNAzyme for the determination of lead ion was developed. The ECL biosensor was fabricated by covalently coupling 5′-amino-DNAzyme-tagged with ruthenium bis (2,2′-bipyridine) (2,2′-bipyridine-4,4′-dicarboxylic acid)-ethylenediamine (Ru1-17E′) onto the surface of graphite electrode modified with 4-aminobenzoic acid, and then a DNA substrate with a ribonucleotide adenosine hybridized with Ru1-17E′ on the electrode. Upon binding of Pb²⁺ to the Ru1-17E′ to form a complex which catalyzed the cleavage of the DNA substrate, the double-stranded DNA was dissociated and thus led to a high ECL signal. The signal linearly increases with the concentration of Pb²⁺ in the range from 5.0 to 80 pM with a detection limit of 1.4 pM and a relative standard derivation of 2.3%. This work demonstrates that using DNAzyme tagged with ruthenium complex as an ECL probe and covalently coupling method for the fabrication of the ECL biosensor with high sensitivity, good stability and significant regeneration ability is promising approach.     

Ligandless temperature-controlled ionic liquid-phase microextraction of lead(II) ion prior to its determination by FAAS

We describe the application of temperature-controlled ionic liquid based microextraction (TC-IL-ME) of lead(II) ion. The method does not require the use of an organic solvent or a ligand. Rather, the IL is directly added to the aqueous sample containing Pb(II) in a centrifuge tube, and the mixture is heated to 80 °C for 4 min. After cooling at 0 °C, the solution turns cludy due to the formation of fine droplets of the IL containing Pb(II). The IL is separated by centrifugation, acidified, and directly submitted to FAAS by microinjection. The effects of pH value, volume of IL, extraction time, temperature, sample volume and matrix were optimized to result in a preconcentration factor of 30, a detection limit of 5.8 μg L^?1, and a limit of quantification of 19.3 μg L^?1. The method was validated by analyzing a certified reference material (NCSZC81002B; hair). A recovery test performed with spiked samples gave values between 102 % and 105 %. The method was also used to determine Pb(II) in hair samples.

The reaction of the trichloromethylium ion with olefins

The reactions of [CCl₃]⁺ with ethylene, 1-hexene, cyclopentence, cyclohexene and styrene have been studied in a field-free, high-pressure ion source by time-resolved ion collection following a short ionizing pulse of electrons. Ethylene is completely unreactive, while addition of [CCl₃]⁺ to the olefinic bond of the other compounds is followed by loss of one or more HCl molecules to give unsaturated cations. Only styrene forms a stable adduct [MCCl₃]⁺ which is an arenium ion produced by addition to the aromatic ring. Rate constants for the reaction of [CCl₃]⁺ have been determined and show that whereas reaction with styrene occurs at almost every ion-molecule collision, with 1-hexene and cyclopentene only 15% of the collisions lead to reaction.     

Surfactant-assisted transport of lead ion through a bulk liquid membrane containing dicyclohexyl-18-crown-6: efficient removal of lead from blood serum and sea water

The selective and efficient surfactant assisted transport of Pb²⁺ ions using a bulk liquid membrane composed of dicyclohexyl-18-crown-6, as a highly selective carrier, in chloroform solution is reported. In the presence of 6.0 × 10^?2 M P₂O₇ ^4? ions and 10^?3 M sodium dodecylsulfate, as suitable stripping agent and membrane/receiving phase interface modifier, respectively, in the receiving phase and 2.4 × 10^?3 M picric acid, as a counter ion in the source phase, the amount of lead transported across the liquid membrane after 5 h is 100.0 ± 1.1. The designed transport system was successfully applied to the removal of lead from sea water and blood serum samples.     

Synthesis of calcium alginate nanoparticles for removal of lead ions from aqueous solutions

Calcium alginate nanoparticles (CANPs) were synthesized to remove lead ion [Pb(??)] as pollutant of environment from aqueous solutions. The produced CANPs were characterized by Fourier transform infrared spectroscopy (FTIR), particle size analysis (PSA) and scanning electron microscope (SEM). Various factors, which affected adsorption efficiency of lead ions by CANPs, such as pH (pH from 1 to 8), initial ions concentration (in the range of 25 to 125 mg L^–1), contact time (varying from 5 to 120 min), and adsorbent dose (50 to 500 mg L^–1), were investigated for determination of optimum experimental conditions. The result of tests showed that the investigated factors had significant effects on adsorption of Pb(??) ions and the maximum adsorption percentage of lead at pH = 6~7, 25 mg L^–1 initial ions concentration, contact time of more than 140 min. and for adsorbent dose at 500 mg L^–1. Also these results demonstrated the effective adsorption of Pb²⁺ ions by synthesized CANPs that occurred due to a high surface area of CANPs and the presence of anionic carboxylate functional groups and allowed effective absorbing and removing Pb(??) ions from aqueous solutions. Thus, these nanoparticles were able to remove over 99% of lead ions from solution.     

Gas phase ion/molecule reactions in phosphine/germane mixtures studied by ion trapping

Gaseous mixtures of phosphine and germane have been investigated by ion trap mass spectrometry. Reaction pathways together with rate constants of the main reactions are reported. The mechanisms of ion/molecule reactions have been elucidated by single and multiple isolation steps. The GeH_n⁺ (n = 1–3) ions react with phosphine to give GePH_n⁺ (n = 2–4) ions. The GePH₄⁺ ion further reacts with GeH₄ to yield Ge₂PH₆⁺. The GePH_n⁺ (n = 2–4) mixed ionic family also originates from the P⁺ phosphine primary ion, as well as from the P₂H_n⁺ (n = 0–3) secondary ions of phosphine reacting with neutral germane and from Ge₂H₂⁺ reacting with phosphine. The main reaction pathways of the PH_n⁺ (n = 0–2) ions with GeH₄ lead to the formation of the GeH₂⁺ and GeH₃⁺ ionic species. Protonation of phosphine from different ionic precursors is a very common process and yields the stable phosphonium ion, PH₄⁺. Trends in total abundances of secondary GePH_n⁺ (n = 2–4) ions as function of reaction time for different PH₃/GeH₄ pressure ratios show that excess of germane slightly affects the nucleation of mixed Ge-P ions.     

Spectrophotometric detection of lead(II) ion using unimolecular peroxidase-like deoxyribozyme

Deoxyribonucleic acid (DNA) can form G-quadruplexes in the presence of certain metal ions. These play a functional role in a variety of biological process. A DNA 17-mer (PW17) was previously reported to bind hemin in the presence of excess potassium ion. The resulting stabilized G-quadruplex-hemin complex exhibits peroxidase-like activity. However, this activity is lost in the presence of one equivalent of Pb²⁺ ion. We exploit this property in a method for spectrophotometric detection of Pb²⁺. Inhibition by Pb²⁺ ion is reflected by a change in the Soret band of hemin and a sharp reduction in the catalytic activity towards hydrogen peroxide-mediated chromogenic oxidation of 2,2′-azino-bis(3-ethylbenzothiazoline)-6-sulfonate. The new method enables Pb²⁺ to be detected in the concentration range from 0.05 to 1.2 μM, with a detection limit of 27 nM. The assay shows high selectivity over other metal ions. It was successfully used to determine Pb²⁺ in water samples.     

Swift heavy ion induced effects at Mo/Si interface and silicide formation

Swift heavy ion (SHI) induced modification at metal/Si interfaces has emerged as an interesting field of research due to its large applications. In this study, we investigate SHI‐induced mixed molybdenum silicide film with ion fluences. The molybdenum thin films were deposited on silicon substrates using e‐beam evaporation at 10^?8 torr vacuum. Thin films were irradiated with Au ions of energy 120 MeV to form molybdenum silicide. The samples were characterized by grazing incidence X‐ray diffraction (GIXRD) technique for the identification of phase formation at the interface. Rutherford backscattering spectrometry (RBS) was used to investigate the elemental distribution in the films. The mixing rate calculations were made and the diffusivity values obtained lead to a transient melt phase formation at the interface according to thermal spike model. Irradiation‐induced effects at surface have been observed and roughness variations at the surface were calculated using atomic force microscopy (AFM) technique. Copyright © 2009 John Wiley & Sons, Ltd.     

Determination of lead (II) ion by highly selective and sensitive lead (II) membrane electrode based on 2-(((E)-2-((E)-1-(2-hydroxyphenyl) methyliden)hydrazono)metyl)phenol

A PVC (poly vinyl chloride) membrane electrode for lead ion based on 2-(((E)-2-((E)-1-(2-hydroxyphenyl)methyliden)hydrazono)metyl)phenol (HMHMP) as a membrane carrier was prepared. This electrode exhibited linear response with Nernstian slope of 29.2?±?0.2?mV per decade within the concentration range of 2.0?×?10^?7–1.0?×?10^?1?M lead ion. The limit of detection, as determined from the intersection of the extrapolated linear segments of the calibration plot, was 8.0?×?10^?8 M. The electrode exhibited high selectivity for Pb (II). The response time of the electrode was about 5–10?s for different concentrations. The electrode is suitable for use in aqueous solutions in a pH range of 5.0–7.5. It was used as an indicator electrode in a titration of Pb (II) with chromate at constant pH. This electrode was used for the determination of lead in ore samples, and the results were in agreement with those obtained with an atomic absorption spectroscopy (AAS) method. Also lead selective electrode was used for monitoring of lead in spiked samples of the Zayanderud River and waste water by the potentiometry technique.     

Highly selective recognition of lead ion in water by a podand fluoroionophore/gamma-cyclodextrin complex sensor

We report herein a novel podand fluoroionophore/gamma-cyclodextrin (gamma-CyD) complex sensor that shows markedly high selectivity for lead (Pb2+) ion in water.     

Preparation of a miniaturised iodide ion selective sensor using polypyrrole and pencil lead: effect of double-coating, electropolymerisation time, and current density

Polypyrrole (PPy) is a conducting polymer which can be used for producing different ion-selective electrodes. An iodide-doped (PPy-iodide) was prepared electrochemically by anodic polymerisation of pyrrole in the presence of an iodide ion in an aqueous solution on the surface of a pencil lead. Polymerisation was investigated under galvanostatic conditions. The effects of electropolymerisation conditions on the characteristics of the potential response of the sensor were examined. Concentrations of pyrrole, iodide ions, and conditioning solution plus current density and the time of electropolymerisation were optimised in relation to the slope and linearity of calibration graphs. This electrode showed a Nernstian behaviour of 61.1 mV per decade for I^? ion over a wide concentration range from 1.0 × 10^?5 M to 1.0 × 10^?1 M, with the limit of detection of 9.3 × 10^?6 M. The response time of the electrode was from 3–5 s. The selectivity coefficients of the prepared sensors over a wide spectrum of interference anions were also evaluated, revealing that selectivity improves as a result of double-coating with PPy. A similar improvement was observed under lower current density and longer electropolymerisation time. This sensor was applied in the determination of iodide ions using titration potentiometry. This electrode can be used for the determination of iodide in drug preparations.     

Wide linear range nanomaterial/ionophore-based electrode used for determination of lead in environmental and biological samples with differential pulse voltammetry

A new chemically modified carbon paste electrode is fabricated to determine lead ion concentration in its trace level in aqueous media with differential pulse voltammetry (DPV). The best performance is obtained by the carbon paste electrode composition including 20% of dithiodibezoic acid (DDA), 80% of high purity graphite powder and 60?µL of colloidal gold nanoparticle (AuNP) solution. The proposed electrode has a wide linear calibration response from 1?×?10^?9 to 6?×?10^?5 M with a detection limit of 6.6?×?10^?10?M, at pH 3.5. Seven replicate determination of 5?×?10^?8?M of lead ion concentration gives a relative standard deviation of 3.33%. The modified sensor is applied to determine lead contents in some environmental and biological Samples with satisfactory results.     

On/off fluorescence switch of a calix[4]arene by metal ion exchange

A new calix[4]arene-based fluorescence chemosensor displaying a strong excimer emission was prepared. When a Pb²⁺ ion is bound to the two amide oxygen atoms linked to the fluorophores, the ligand exhibits a marked quenched excimer emission due to its geometrical change during the complexation. By the addition of Ca²⁺ ion into the 1·Pb²⁺, the excimer emission band was revived, by which an interesting on/off switch process is proposed.     

Dielectric relaxation losses in lead chloride and lead bromide: Localized dipoles

A further analysis of previous reported measurements of dielectric relaxation losses in lead chloride and lead bromide crystals shows that the dipoles may occupy several energetically different positions, giving rise to localization of the dipoles and anomalous behaviour of the susceptibility. This energy difference is determined. Inspection of the crystal structure shows that the anion vacancy, being the mobile part of the dipole (which is an associate like (Me_Pb·V_X)^x or (O_X·V_X)^x where X = Cl, Br), may jump indeed between halide ion sites with different coordination number.A comparison between the dipole concentration as calculated from the observed losses and the associate concentration as estimated from ionic conductivity experiments leads to the conclusion that local field corrections in the calculations are important.     

Electrochemical detection of blood lead based on the enhancement effect of copper

The anodic stripping peak current of lead on the glassy carbon electrode surface was greatly increased in the presence of high concentration of copper ion. The effects of supporting electrolyte, concentration of Cu²⁺, accumulation potential and accumulation time were studied on the stripping peak current of Pb²⁺. As a result, a sensitive, simple and rapid electrochemical method was developed for the detection of lead. In 0.01 M HNO₃ solution containing 800 g,g L^?1 Cu²⁺, the stripping peak current of Pb²⁺ increases linearly with its concentration over the range from 2 to 100 μg L^?1. The detection limit is 1 μg L^?1 after 4-min accumulation at ?0.8 V. It was used to detect the concentration of lead in blood samples, and the results consisted with the values that obtained by atomic absorption spectrometry.     

Electrical conductance,density and viscosity of the system lead(II) dodecanoate/dodecanoic acid

Data are presented for the densities, electrical conductances and viscosities of the molten system lead(II) dodecanoate/dodecanoic acid. Over the concentration range studied, molar volumes are linear functions of concentration at any selected temperature, although there are indications of deviations from ideal behaviour over the complete composition range from pure soap to pure acid. The molar volumes of the system lead(II) carboxylate/carboxylic acid for the even chain acids C₁₀ to C₁₈ are linear functions of chain length. As with other lead(II) dodecanoate systems, the Arrhenius plots for the conductance of the mixtures show curvature.Activation energies for conductance in the low temperature region show a steady decrease with increasing mole fraction of the acid. It is suggested that this arises largely from the increased mobility of the Pb²⁺ ion. The activation energies for viscous flow in the mixtures are similar to that of pure lead dodecanoate. Studies of the viscosities of the system lead(II) carboxylate/carboxylic acid as a function of the temperature for the even chain length acids C₁₀ to C₁₈ suggest a slight decrease in size of the unit of viscous flow when acid is present.     

An ion trap-ion mobility-time of flight mass spectrometer with three ion sources for ion/ion reactions

This instrument combines the capabilities of ion/ion reactions with ion mobility (IM) and time-of-flight (TOF) measurements for conformation studies and top-down analysis of large biomolecules. Ubiquitin ions from either of two electrospray ionization (ESI) sources are stored in a three dimensional (3D) ion trap (IT) and reacted with negative ions from atmospheric sampling glow discharge ionization (ASGDI). The proton transfer reaction products are then separated by IM and analyzed via a TOF mass analyzer. In this way, ubiquitin +7 ions are converted to lower charge states down to +1; the ions in lower charge states tend to be in compact conformations with cross sections down to ～880 Ų. The duration and magnitude of the ion ejection pulse on the IT exit and the entrance voltage on the IM drift tube can affect the measured distribution of conformers for ubiquitin +7 and +6. Alternatively, protein ions are fragmented by collision-induced dissociation (CID) in the IT, followed by ion/ion reactions to reduce the charge states of the CID product ions, thus simplifying assignment of charge states and fragments using the mobility-resolved tandem mass spectrum. Instrument characteristics and the use of a new ion trap controller and software modifications to control the entire instrument are described.     

Ion manipulation and enrichment mass spectrometer for cleavage of disulfide bond via ion/ion reaction

A novel mass spectrometer with the capability of ion manipulation and enrichment was developed to perform gas‐phase ion/ion reactions followed by product ions accumulation. The development of this apparatus opens opportunities for more complex sequences of ion manipulations, thus offers the potential on extensive application involving ion/ion reaction. Here, cleavage of disulfide bond in peptide was demonstrated based upon this ion manipulation and enrichment mass spectrometer. Two typical peptides including S‐glutathionylated ARACAKA with an intermolecular disulfide bond, and oxytocin with an intramolecular disulfide bond were chosen as typical samples to demonstrate the ability of the apparatus. After ion/ion reaction between selected peptide cations and periodate ions (IO₄^?), two kinds of product ions (eg, [M + O + H]⁺ and [M + H + Na + IO₄]⁺) were enriched with a number of accumulation events. Afterwards, the enriched ions were subjected to activation, and the disulfide bond cleavage was clearly observed from the tandem mass spectra. These results illustrate the potential of this apparatus for ion manipulation performing ion/ion reaction, and low abundance product ion enrichment.