Sonoelectrochemistry in Acoustically Emulsified Media: The Detection of Lead

The double extraction of target lead ions which are then voltammetrically quantified via acoustically assisted anodic stripping voltammetry is demonstrated. The technique involves first the extraction of lead from the aqueous volume into an organic phase containing the ligand dithizone (diphenylthiocarbazone). Second, the chelated lead is then stripped into a clean electrochemically clean aqueous solution where the lead from the original solution can be quantified. This method is shown to be applicable in electrochemically fouling media, providing a high sensitivity with a limit of detection for lead in the order of 10^?7 mol dm^?3. A theoretical extraction model is presented for the optimal conditions of extraction. The technique is applied to the analysis of lead in wine samples offering quantitative data, which is in good agreement with those obtained from an independent technique (AAS).     

Biosorption of copper by biomass of extremophilic algae

Copper and lead are among the most important chemical pollutants of the environment including hydrosphere. Interaction of these heavy metals with biomass of aquatic plant organisms including algae is an area of active research in ecological chemistry. We investigated the interaction of the biomass of unique extremophilic (thermophilic) algae Galdieria sulphuraria with these heavy metals in aquatic environment using stripping voltammetry. Biosorption of copper by the studied biomass from aquatic medium has been discovered; however, no biosorption of another heavy metal from aquatic environment with the biomass has been detected. The experiments with the mortmass of Galdieria sulphuraria have revealed no sorption of the heavy metals as measured by stripping voltammetry. The difference in the interaction of copper and lead with the algal biomass is important for deeper understanding of the biosorption phenomenon. The new data stimulated further interest to the concept of biogenic migration of chemical elements that was proposed by V.I. Vernadskii. The results contributed to the scientific basis for innovative biotechnology to decontaminate water.     

The determination of trace amounts of zinc, cadmium, lead and copper in airborne particulate matter by anodic stripping voltammetry

The application of anodic stripping voltammetry, with a hanging mercury drop electrode, to the determination of zinc, cadmium, lead and copper in airborne particulate matter collected by filtration is discussed. This procedure allows for the destruction of the filter material followed by the complete dissolution (including silicates) of the collected particulate matter. A low-temperature ashing process is described and the recovery of cadmium in this procedure is studied. Analytical data obtained by anodic stripping and atomic absorption for zinc, cadmium, lead and copper are compared.     

Use of a modified, high-sensitivity, anodic stripping voltammetry method for determination of zinc speciation in the North Atlantic Ocean

Zinc speciation is considered to be an important determinant of the biological availability of zinc. Yet in oceanic surface waters, characterization of zinc speciation is difficult due to the low concentrations of this essential micronutrient. In this study, an anodic stripping voltammetry method previously developed for the total determination of cadmium and lead was successfully adapted to the measurement of zinc speciation. The method differs from previous zinc speciation anodic stripping voltammetry methods in that a fresh mercury film is plated with each sample aliquot. The fresh film anodic stripping voltammetry method was compared to competitive ligand exchange cathodic stripping voltammetry in a profile from the North Atlantic Ocean. Results using the fresh film anodic stripping voltammetry method were similar to those determined using the cathodic stripping voltammetry method, though ligand concentrations determined by fresh film anodic stripping voltammetry were generally slightly higher than those determined by cathodic stripping voltammetry. There did not seem to be a systematic difference between methods for the estimates of conditional stability constants. The ligand concentration in the North Atlantic profile ranged from 0.9 to 1.5 nmol L⁻¹ as determined by fresh film anodic stripping voltammetry and 0.6 to 1.3 nmol L⁻¹ as determined by cathodic stripping voltammetry. The conditional stability constants determined by fresh film anodic stripping voltammetry were 10^9.8-10^10.5 and by cathodic stripping voltammetry were 10^9.8-10^11.3.     

Determination of mobile form contents of Zn, Cd, Pb and Cu in soil extracts by combined stripping voltammetry

The amount of mobile forms of Zn, Pb, Cd and Cu in extracts obtained by treating soil samples with ammonium nitrate were determined by an appropriate combination of anodic and cathodic stripping voltammetry with hanging mercury drop electrode. Every analysis required three mercury drops: on the first one, zinc was determined; on the second, cadmium and lead; on the third, copper was determined. Zinc, lead and cadmium were determined by conventional differential-pulse anodic stripping voltammetry. For copper determination, adsorptive differential-pulse cathodic stripping voltammetry with amalgamation using chloride ions as a complexing agent was applied. The standard deviation of the results was from 1 to 10% depending on the metal content in the sample. Voltammetric results were in good agreement with the AAS analysis. No microwave digestion of soil extracts was necessary.     

Optimization and validation of an automated voltammetric stripping technique for ultratrace metal analysis

A new automated batch method for the determination of ultratrace metals (nanogram per liter level) was developed and validated. Instrumental and chemical parameters affecting the performance of the method were carefully assessed and optimized. A wide range of voltammetric methods under different chemical conditions were tested. Cadmium, lead and copper were determined by anodic stripping voltammetry (ASV), while nickel, cobalt, rhodium and uranium by adsorptive cathodic stripping voltammetry (AdCSV). The figures of merit of all of these methods were determined: very good precision and accuracy were achieved, e.g. relative percentage standard deviation in the 4-13% for ASV and 2-5% for AdCSV.The stripping methods were applied to the determination of cadmium, lead, copper, nickel, cobalt, rhodium and uranium in lake water samples and the results were found to be comparable with ICP-MS data.     

Anodic stripping voltammetric determination of antimony in gunshot residue

Anodic stripping voltammetry (a.s.v.) ata mercury film on a glassy carbon working electrode was utilized to determine the amount of antimony from hand swabs. The procedure described is useful for determining 10–120 ng of antimony found in the residue ou the hands of an individual suspected of discharging or handling a firearm. The voltammogram provides an elemental pattern recognizable as gunshot residue containing small amounts of antimony and much larger amounts of copper and lead. The amount of antimony in a variety of gunshot-residue samples was determined by both anodic stripping voltammetry and graphite-furnace atomic absorptiou spectrometry for comparison purposes. Anodic stripping voltammetry is excellent for observation of the multielement pattern which proves to be very useful for gunshot-residue samples.     

Bucky-gel coated glassy carbon electrodes, for voltammetric detection of femtomolar leveled lead ions

Femtomolar (fM) leveled lead ions were electrochemically detected using a bucky-gel coated glassy carbon electrode and differential pulse anodic stripping voltammetry. The bucky-gel was composed of dithizone, ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate), and multi-walled carbon nanotubes (MWCNTs). The fabrication of the bucky-gel coated electrode was optimized. The modified electrode was characterized with voltammetry, electrochemical impedance spectroscopy, and chronoamperometry. After the accumulation of lead ions into the bucky-gel modified electrode at −1.2 V vs. saturated calomel electrode (SCE) for 5 min in a pH 4.4 sodium acetate-acetate acid buffer solution, differential pulse anodic stripping voltammograms of the accumulated lead show an anodic wave at −0.58 V. The anodic peak current is detectable for lead ions in the concentration range from 1.0 μM down to 500 fM. The detection limit is calculated to be 100 fM. The proposed method was successfully applied for the detection of lead ions in lake water.     

Determination of trace amounts of thorium by electroanalytical techniques

Trace amounts of thorium have been determined in the presence of uranyl nitrate and ammonium diuranate (as interferents) by cyclic voltammetry, differential-pulse polarography, differential-pulse voltammetry, square-wave voltammetry and anodic-stripping voltammetry. The determination is based on the substitution of thorium for copper, lead and cadmium in their EDTA complexes and voltammetric measurement of the displaced metal ion. The detection limits ranged between 2 x 10(-7) and 1 x 10(-6)M (r.s.d. 2-7%) for solutions free from the uranium compounds, and between 8 x 10(-7) and 5 x 10(-6)M (r.s.d. 3-5%) in the presence of the uranium compounds at concentrations up to about 1000 times that of thorium. The detection limits depend on both the particular technique and the EDTA complex employed. Anodic-stripping voltammetry gave detection limits of 8 x 10(-8) and 10(-7)M in the absence and presence of uranium respectively.     

Voltammetric method for the determination of Zn,Cd, Pb,Cu and Ni in interstitial water

To determine heavy metals in interstitial water from Baltic sea sediments a sampling method with subsequent voltammetric determination is described. Copper, lead, zinc and cadmium are determined in the UV-digested samples of interstitial water by differential pulse anodic stripping voltammetry while nickel is determined by adsorption voltammetry. The determination of five metals in one sample in a wide concentrations range is possible using a low cost apparatus. The profiles of the metal concentrations in interstitial water of subsequent layers of sediments, sampled from Puck Bay, Gdańsk Bay, the Bornholm area and the S?upsk area are presented.     

Anodic-stripping voltammetry of heavy metals in the presence of organic surfactants

The efficacy of fumed silica for removal of sorption interferences by organic surfactants in the anodic-stripping voltammetry of heavy metals is demonstrated. Appropriate addition of silica to the sample solution rapidly "purifies" it from interfering surfactants during the nitrogen purge step. Up to at least 6 ppm of gelatin, Triton X-100, albumin or Liqui-Nox then does not affect the stripping response of cadmium, lead and zinc at the hanging mercury drop electrode. A relative standard deviation of 5.5% is obtained for 20 successive measurements of 1 x 10(-7)M lead in the presence of 2 ppm Triton X-100. Analogous improvements are observed at the mercury film electrode (in the presence of up to 60 ppm of these surfactants). The use of silica thus possesses the advantages of speed, efficiency, simplicity and low cost compared to other schemes for dealing with surfactant interferences in anodic-stripping voltammetry.     

An assessment of contemporary atomic spectroscopic techniques for the determination of lead in blood and urine matrices

The preparation and validation of a number of clinical reference materials for the determination of lead in blood and urine is described. Four candidate blood lead reference materials (Lots, 047–050), and four candidate urine lead reference materials (Lots, 034, 035, 037 and 038), containing physiologically-bound lead at clinically relevant concentrations, were circulated to up to 21 selected laboratories specializing in this analysis. Results from two interlaboratory studies were used to establish certified values and uncertainty estimates for these reference materials. These data also provided an assessment of current laboratory techniques for the measurement of lead in blood and urine. For the blood lead measurements, four laboratories used electrothermal atomization AAS, three used anodic stripping voltammetry and one used both ETAAS and ICP-MS. For the urine lead measurements, 11 laboratories used ETAAS (most with Zeeman background correction) and 10 used ICP-MS. Certified blood lead concentrations, ±S.D., ranged from 5.9±0.4 μg/dl (0.28±0.02 μmol/l) to 76.0±2.2 μg/dl (3.67±0.11 μmol/l) and urine lead concentrations ranged from 98±5 μg/l (0.47±0.02 μmol/l) to 641±36 μg/l (3.09±0.17 μmol/l). The highest concentration blood lead material was subjected to multiple analyses using ETAAS over an extended time period. The data indicate that more stringent internal quality control practices are necessary to improve long-term precision. While the certification of blood lead materials was accomplished in a manner consistent with established practices, the urine lead materials proved more troublesome, particularly at concentrations above 600 μg/l (2.90 μmol/l).     

Lead Sulfide Nanoparticle as Oligonucleotides Labels for Electrochemical Stripping Detection of DNA Hybridization

We report a method for the detection of DNA hybridization in connection to lead sulfide (PbS) nanoparticle tags and electrochemical stripping measurement of the lead. A kind of lead sulfide nanoparticle with free carboxyl groups on its surface was synthesized in aqueous solution. The nanoparticle was used as a marker to label a sequence‐known oligonucleotide, which was then employed as a DNA probe for identifying a target ssDNA immobilized on a PPy modified electrode based on a specific hybridization reaction. The hybridization events were monitored by the oxidation dissolution of the lead sulfide anchored on the hybrids and the indirect determination of the lead ions by anodic stripping voltammetry (ASV). The detection limit is 0.3 pmol L^?1 of target oligonucleotides. The PbS nanoparticle combining its easy conjugation to the DNA molecule with the highly sensitive stripping voltammetry detection of lead shows its promising application in the electrochemical DNA hybridization analysis assay.     

Determination of lead in blood by hydrodynamic voltammetry in a flow injection system with wall-jet detector

Lead is one of the most widely distributed toxic heavy metals in the environment. It is a cumulative poison, affecting the brain and nervous system. The threshold between the normal lead level and the level where physiological effects become manifest is relatively narrow. It is therefore desirable to screen exposed populations in order to identify the danger in time. The lead concentration in the blood is a measure to the total amount of lead in the body. A fast, accurate and cheap method for the determination of lead in blood is therefore needed. The conventional method used to determine lead in blood is atomic absorption. Electrochemical methods like stripping voltammetry combine high analytical sensitivity with relatively low cost for the equipment; however, electrode preparation is critical for the success of an analysis, and highly skilled personnel are needed. We describe an automated electrochemical method, using flow injection analysis with a wall-jet detector. Lead is released from its binding site in the blood by ion exchange and quantified by stripping voltammetry with a mercury film electrode (MFE). The method allows for the detection of 0.05 ppm Pb(2+) with an accuracy of about 10%. Electrode poisoning by proteins from the blood can be effectively suppressed when a MFE modified with a Nafion(R)-membrane coating is used. Such modified electrodes can be activated in the solution without further treatment, and used for more than 100 analyses before they have to be replaced. A solid matrix MFE with a Nafion(R)-membrane and all necessary chemicals for mercury film formation and lead release has been developed. Such electrodes are discussed as disposable electrodes for a portable blood lead detector.     

Combined micro-droplet and thin-film-assisted pre-concentration of lead traces for on-line monitoring using anodic stripping voltammetry

An improved analytical method for airborne lead traces is reported. It is based on using a Venturi scrubber sampling device for simultaneous thin-film stripping and droplet entrapment of aerosol influxes. At least threefold enhancement of the lead-trace pre-concentration is achieved. The sampled traces are analyzed by square-wave anodic stripping voltammetry. The method was tested by a series of pilot experiments. These were performed using contaminant-controlled air intakes. Reproducible calibration plots were obtained. The data were validated by traditional analysis using filter sampling. LODs are comparable with the conventional techniques. The method was successfully applied to on-line and in situ environmental monitoring of lead.     

铅镧和铅钐合金在硫酸溶液中生长的阳极膜性质的研究

应用交流伏安法和线性电位扫描法研究了Pb ,Pb 1.0at%La和Pb 1.0at%Sm电极在硫酸溶液中以 0 .9V(vs .Hg/Hg2 SO4 )生长的阳极Pb(Ⅱ )膜增长率和膜的阻抗实部变化 ,并采用循环伏安法研究了它们在 0 .6～ 1.6V(vs.Hg/Hg2 SO4 )间的循环伏安特性 ,结果表明 :在铅中添加Sm有利于抑制铅的阳极腐蚀和降低阳极Pb(Ⅱ )膜的阻抗 ,La亦可降低阳极Pb(Ⅱ )膜的阻抗 ,但其作用不如Sm明显     

Contribution of migration current to the voltammetric deposition and stripping of lead with and without added supporting electrolyte at a mercury-free carbon fibre microdisc electrode

In order to assess the contribution and analytical significance of migration, electrochemical studies on the deposition and stripping of lead at a carbon fibre microelectrode (diameter of 10 μm) have been undertaken in aqueous solutions containing 1 mM lead ions with variable KNO₃ supporting electrolyte concentrations (10⁻¹ to 10⁻⁵ M), as well as in the total absence of deliberately added supporting electrolyte. The methodology involved the application of cyclic voltammetry to characterise the Pb²⁺ (solution)+2e⁻Pb (metal) process in both the reduction (Pb deposition) and stripping (Pb dissolution) directions. The use of a mercury-free carbon surfaces means that the lead stripping does not occur from the amalgam state, as is commonly the case in anodic stripping voltammetry. In the deposition step, the current rises sharply with potential in response to a lead nucleation-growth process and then reaches an almost potential independent limiting value. The stripping step, obtained on the reverse scan, exhibited oxidation peak currents resulting from the redissolution or stripping of the metal from the electrode surface. The influence of the electrolyte concentration and hence migration current at −0.8 V versus Ag/AgCl for the deposition process, as well on the redissolution peak current and the dependence of the voltammograms on scan rate (10–1000 mV) are discussed. Interestingly, neither deposition limiting nor stripping peak currents vary in a simple manner with added supporting electrolyte concentrations, with maximum values being observed at 10⁻⁵ M rather than zero concentration of added KNO₃. An important implication for the voltammetric determination of lead in low ionic strength media by the very sensitive technique of anodic stripping voltammetry is that use of the method of standard additions commonly employed to minimise unknown matrix problems, is prone to error when contributions to the process from migration current are important.     

Investigation of the electrochemical behaviour of lead dioxide in aqueous sulfuric acid solutions by using the in situ EQCM technique

The charge-discharge characteristics and the aging mechanism of PbO₂ layers in contact with sulfuric acid solutions of different concentrations (1.5–5.0 M) were studied by using combined cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM) techniques. For this purpose, thick lead dioxide layers were electrodeposited on gold substrate from aqueous solutions of Pb(NO₃)₂ dissolved in nitric acid. Based on the electrochemical and the mass change responses, it was found that in more concentrated solutions of H₂SO₄, the main reduction reaction was the transformation of lead dioxide to lead sulfate. However, in less concentrated sulfuric acid media, the transformation of lead dioxide to lead(II) ion became the main reaction. These Pb²⁺ ions transformed into lead sulfate crystals later by a chemical reaction. Because the electrochemical oxidation of lead sulfate is less favourable in sulfuric acid medium of higher concentrations, thus, PbO₂ layers cannot be tested by continuous cyclization, which is necessary to study their aging parameters. Therefore, a delay step before each cyclic voltammogram was applied while the non-conductive lead sulfate dissolves or alternatively, by applying a pre-oxidation step prior to each cyclic voltammetry experiment to produce electrochemically significant amount of lead dioxide which can be reduced during the following negative potential sweep.

     

Simplifying the evaluation of graphene modified electrode performance using rotating disk electrode voltammetry

Graphene modified electrodes have been fabricated by electrodeposition from an aqueous graphene oxide solution onto conducting Pt, Au, glassy carbon, and indium tin dioxide substrates. Detailed investigations of the electrochemistry of the [Ru(NH(3))(6)](3+/2+) and [Fe(CN)(6)](3-/4-) and hydroquinone and uric acid oxidation processes have been undertaken at glassy carbon and graphene modified glassy carbon electrodes using transient cyclic voltammetry at a stationary electrode and near steady-state voltammetry at a rotating disk electrode. Comparisons of the data with simulation suggest that the transient voltammetric characteristics at graphene modified electrodes contain a significant contribution from thin layer and surface confined processes. Consequently, interpretations based solely on mass transport by semi-infinite linear diffusion may result in incorrect conclusions on the activity of the graphene modified electrode. In contrast, steady-state voltammetry at a rotating disk electrode affords a much simpler method for the evaluation of the performance of graphene modified electrode since the relative importance of the thin layer and surface confined processes are substantially diminished and mass transport is dominated by convection. Application of the rotated electrode approach with carbon nanotube modified electrodes also should lead to simplification of data analysis in this environment.