Stripping Of Lead Research Articles

A study of the preconcentration and stripping voltammetry of Pb(ii) at carbon electrodes

Both glassy carbon electrodes and carbon fibre microelectrodes were shown to accumulate Pb2+ ions at open circuit, the amount of Pb2+ accumulated being determined by anodic stripping voltammetry in 0.1 M HCl following the accumulation step. The mechanism of Pb2+ accumulation was investigated by studying the effects of the pH of the solution, the concentration of Pb2+ and the preconcentration time on the amount of Pb2+ accumulated. For a 5 min preconcentration time at open circuit, using a glassy carbon electrode (4 mm diameter) and a carbon fibre microelectrode (8 mm diameter), detection of around 10 nM Pb2+ was obtained for both electrodes. The pH dependence of the amount of Pb2+ accumulated suggests that the Pb2+ ions are complexed by carboxylate groups at the surface of the carbon electrodes. This conclusion is supported by results obtained using basal plane and edge plane pyrolytic graphite electrodes and by studies of the effects of electrochemical oxidation of the glassy carbon surface on the magnitude of the lead stripping peak.

Limitations of the use of the electrochemical quartz crystal microbalance in stripping analysis of lead(II) and cadmium(II) on a quartz crystal platinum electrode with a thin mercury film

An electrochemical quartz crystal microbalance (EQCM) with vapour deposited platinum electrodes was used as a support for a 150nm mercury film. This EQCM was then used as a stripping detector for lead(II) and cadmium(II) in 0.2M acetate buffer. Lead concentrations down to 1μgl−1 and cadmium concentrations down to 2μgl−1 could be measured but with limited precision only due to the composite electrode construction, that is, mercury deposited on platinum. Non-mass frequency changes relating to changes in density and viscosity of the mercury film during the stripping of lead and cadmium were not observed under the above conditions.

Sonoelectrochemically modified electrodes: ultrasound assisted electrode cleaning, conditioning, and product trapping in 1-octanol/water emulsion systems

Electrode processes for three types of water soluble redox systems in the presence of power ultrasound have been studied in a non-conventional environment: the 1-octanol/water microemulsion. The capability of ultrasound both to emulsify instantly a liquid/liquid system in the absence of stabilizing agents and to generate a high flux of material towards the electrode surface is shown to provide new tools for the control of electrochemical redox processes. First, the electrochemical reduction of Ru(NH 3) 3+ 6 has been studied. This is known to be a fast and reversible process at a glassy carbon electrode in aqueous 0.1 M KCl even in the presence of ultrasound. The addition of 1-octanol does not significantly affect this redox process up to a very high 1-octanol content in the emulsion system, although a thin film or adsorbed layer of 1-octanol is believed to be present at the electrode surface. Surprisingly, the limiting current and voltammetric characteristics of the reduction process remain nearly unaffected, until, at a critical ratio of ca. 50 vol% 1-octanol, the voltammetric response suddenly disappears, attributed to loss of conductivity in the bulk liquid. Second, and in contrast, the reduction and deposition of Pb 2+ from aqueous 0.1 M HClO 4 at a glassy carbon electrode is strongly affected even by small quantities of 1-octanol, again consistent with a thin layer of 1-octanol being permanently present at the electrode/emulsion interface. With increasing quantities of added 1-octanol the reduction process is gradually shifted several hundred mV to more negative potentials whereas the anodic lead stripping response is first shifted to more positive potentials and finally disappears. Third, the reduction of cobalticinium, CoCp + 2 (Cp= η 5−C 5H 5), in aqueous 0.1 M KOH under silent conditions results in the formation of nearly insoluble, neutral cobaltocene which precipitates at the glassy carbon electrode surface. In the presence of 1-octanol the neutral product dissolves in the organic liquid and allows voltammetric experiments to be conducted without loss of electrode activity due to blocking. The efficiency and the mechanism of this product ‘trapping’ process in the presence of 1-octanol is discussed.

Imaging of the In Situ Deposition of Lead on Highly Oriented Pyrolytic Graphite by Scanning Tunneling and Atomic Force Microscopies

The electrodeposition and stripping of lead has been studied by in situ and ex situ scanning tunneling microscopy (STM) and in situ atomic force microscopy (AFM). The lead was electrodeposited on highly oriented pyrolytic graphite (HOPG). The HOPG was initially treated to produce monolayer deep pits which served as markers and supplied a high density of edge sites. Pb deposits preferentially formed at step and pit edges and resembled crystallite growth on a microelectrode disk. We discuss effects of tip potential on deposition during in situ STM and compare these results with AFM studies. After stripping, scanning microscopy and x‐ray photoelectron spectroscopy indicated that residual Pb species remained on the surface.

Electrodissolution and Electrodeposition of Lead in an Acidic Room Temperature Chloroaluminate Molten Salt

The electrodissolution of a lead rotating disk electrode and the electrodeposition and stripping of lead at a glassy carbon electrode were studied in the 66.7‐33.3 mole percent (m/o) aluminum chloride‐1‐methyl‐3‐ethylimidazolium chloride molten salt at 40°C. The electrodissolution of lead to produce lead(II) is a quasireversible process with an anodic transfer coefficient and a formal heterogeneous rate constant of and , respectively. The electrodeposition of lead on glassy carbon from solutions of exhibits progressive three‐dimensional nucleation with diffusion‐controlled growth of the nuclei. The stripping of lead from this electrode proceeds with 100% efficiency. The formal potential of the Pb2+/Pb couple is , and the diffusion coefficient and Stokes‐Einstein product for lead(II) are and .

Anodic stripping voltammetry at mercury films deposited on ultrasmall carbon-ring electrodes

Abstract : Anodic stripping voltammetry of lead and cadmium without deliberately added electrolytes has been studied at ultrasmall carbon ring electrodes following in situ deposition of mercury. The stripping of lead has been studied in detail to investigate the dependence of stripping peak current on experimental parameters such as potential scan rate, preconcentration duration, deposition potential, concentration of Hg + during deposition and concentration of Pb 2+. Anodic stripping voltammetry in solutions without deliberately added supporting electrolyte avoids problems associated with impurities introducing when electrolyte is added. These impurities appear to be highly important when Pb 2+ analysis is carried out in dilute solutions. In addition, a unique effects is observed when relatively low concentrations of Hg+ are used for the in situ deposition step. When low Hg+ concentrations are used, the stripping current does not decrease as rapidly as expected as the concentration of Pb 2+ is reduced. Keywords: Stripping voltammetry, Ultrasmall carbon ring electrodes.

Automated electrochemical stripping of copper, lead, and cadmium in seawater

Fast staircase stripping at rotating-disk, ring-disk, and split-disk electrodes has been compared with potentiometric, linear scan, and differential pulse stripping for the analysis of Cd, Pb, and Cu in seawater at the mercury film electrode using a purpose-built hard-wired instrument designed for field work. The dependence of rapid staircase stripping peak currents on the staircase parameters at short step widths (> 1 ms) was in agreement with theory for Cd and Pb but not for Cu, suggesting interference from following chemical reactions in the latter case. The technique is much faster than differential pulse stripping and can be carried out in a stirred solution making it better suited for field work. Discrimination of faradaic from capacitance currents is comparable with differential pulse in the case of Cu but is a little poorer in the case of Cd. The performance of the rapid staircase can be improved by the use of a split-disk electrode. The rapid staircase technique is not, however, suitable for use in low ionic strength waters. The performance of the potentiometric stripping technique is critically dependent on the nature of the background subtraction procedure employed.

Electrochemical reduction of the trimethyllead(IV) cation in seawater

The need to distinguish between inorganic and organic forms of lead in seawater has been widely recognized. Electrochemical techniques based on reduction at mercury electrodes or anodic stripping voltammetry have been proposed as methods for determining the various forms of lead. However, detailed investigation of the electrode process for the electrochemical reduction of the trimethyllead cation in seawater show that correct data may not necessarily be obtained with all electrochemical techniques. On the short time scale of polarography the proposed reduction mechanism is: (CH 3) 3Pb ++ e(CH 3) 3Pb+3 Hg→Pb(amalgam)+3 CH 3Hg(ads) 3 CH 3Hg(ads)+3 e→3 CH 3Hg − Data show that differential pulse polarography can be used to determine simultaneously inorganic lead and the trimethyllead cation, however, with inverse oxidation experiments involving stripping of lead (amalgam) such as reverse normal pulse voltammetry, substantial modification to the electrode process occurs in the presence of methylated mercury. Anodic stripping voltammetry therefore suffers from substantial interference, when using the: Pb(amalgam)Pb 2++2 e electrode process for determining the concentration of the trimethyllead cation in seawater.

The separation of lead from copper by co-extraction and selective stripping by LIX 64N

The extraction and stripping of lead from its acetate solution by LIX 64N diluted with Kermac 470B are reported. From these results, a process for the separation of lead from copper by co-extraction and selective stripping has been proposed. Very good co-extraction and selective stripping efficiencies were obtained which indicated that a high degree of separation between copper and lead could be achieved.

Fundamental aspects of lead extraction and stripping by a liquid ion exchange reagent

AbstractLIX 34 liquid ion exchange reagent was introduced commercially by General Mills in 1976. The fundamental aspects of lead extraction and stripping using LIX 34 as the organic extractant in acetic solution has been studied here. Equilibrium isotherms for extraction and stripping, isothermal pH effects, temperature effect, loading capacity and the rate of extraction and stripping on the system Pb2+‐HAc‐LIX 34—Kermac 470B are reported.

Fundamental aspects of lead extraction and stripping by a liquid ion exchange reagent

Fundamental aspects of lead extraction and stripping by a liquid ion exchange reagent

Simultaneous determination of lead, cadmium and zinc in aerosols by anodic stripping voltammetry

The simultaneous determination of lead, cadmium and zinc in air particulate matter by anodic stripping voltammetry is described. Optimum conditions for the anodic stripping of lead, cadmium and zinc were determined using ammonium tartrate buffer at pH 4.5. Interferences from other metals were not encountered and the estimations were reproducible within a standard deviation of ±10%. Low blank values and high sensitivity of the method allowed the determinations at sub-ppb levels with an electrolysis time of 3–10 min. The geometric mean concentrations of lead, cadmium and zinc at various locations in Greater Bombay during 1979 are also presented.

Silver based mercury film electrode part III. Comparison of theoretical and experimental anodic stripping results obtained for lead and copper

The anodic stripping results obtained for lead and copper at an improved model of silver based mercury film electrode (SBMFE) were compared with theoretical predictions given for such a case by de Vries and van Dalen. During the study particular attention was paid to the formation of heterogenous amalgams and to influences which this effect could exert on the shape of the stripping peaks. Under conditions where homogenous amalgams were formed a good agreement was observed between theoretical and experimental results for peak currents ( i p ), shifts of the peak potential ( E p - E 1/2 ) and for half peak-widths ( b 1/2 ) obtained for the stripping of lead. On the other hand, small broadening of the values of b 1/2 and small decreasing of the values of i p were observed for copper compared to theoretical results. For heterogenous amalgams of both metals investigated the anodic displacement of the peak position was observed compared to the position predicted by the theory. The b 1/2 values observed under these conditions could increase, decrease or even stay unchanged depending on the scan rate used. The conditions where the significant increase of concentration of metal deposited into mercury film may lead to enhanced stripping signal were also discussed.

Silver based mercury film electrode: Part III. Comparison of theoretical and experimental anodic stripping results obtained for lead and copper

The anodic stripping results obtained for lead and copper at an improved model of silver based mercury film electrode (SBMFE) were compared with theoretical predictions given for such a case by de Vries and van Dalen. During the study particular attention was paid to the formation of heterogenous amalgams and to influences which this effect could exert on the shape of the stripping peaks. Under conditions where homogenous amalgams were formed a good agreement was observed between theoretical and experimental results for peak currents ( i p), shifts of the peak potential ( E p- E 1/2) and for half peak-widths ( b 1/2) obtained for the stripping of lead. On the other hand, small broadening of the values of b 1/2 and small decreasing of the values of i p were observed for copper compared to theoretical results. For heterogenous amalgams of both metals investigated the anodic displacement of the peak position was observed compared to the position predicted by the theory. The b 1/2 values observed under these conditions could increase, decrease or even stay unchanged depending on the scan rate used. The conditions where the significant increase of concentration of metal deposited into mercury film may lead to enhanced stripping signal were also discussed.

Discharge-ionization of metals on an indifferent electrode

Summary The method of inverse (film) voltammetry of solid phases is suggested for use in studying the system of an indifferent electrode-metal-metal salt solution. In this way information is obtained about the character of the relations between the metal and the electrode, the metal distribution on the electrode surface, and the difference between the properties of a metal deposit and the corresponding macrophase. The systems graphite electrode-bismuth-bismuth salt solution and graphite electrode-lead-lead salt solution are studied experimentally. The polarograms of lead stripping from a platinum electrode surface are obtained. The relation between the character of the dependence of the potential of the system on the logarithm of concentration of potential-determining ion in solution and the shape of anodic polarograms is found. The facts observed experimentally are accounted for by the assumption of the possibility of ad-atom formation and the growth of the metal phase layer in the deposition process on an indifferent solid electrode.

Discharge-ionization of metals on an indifferent electrode

The method of inverse (film) voltammetry of solid phases is suggested for use in studying the system of an indifferent electrode-metal-metal salt solution. In this way information is obtained about the character of the relations between the metal and the electrode, the metal distribution on the electrode surface, and the difference between the properties of a metal deposit and the corresponding macrophase. The systems graphite electrode-bismuth-bismuth salt solution and graphite electrode-lead-lead salt solution are studied experimentally. The polarograms of lead stripping from a platinum electrode surface are obtained. The relation between the character of the dependence of the potential of the system on the logarithm of concentration of potential-determining ion in solution and the shape of anodic polarograms is found. The facts observed experimentally are accounted for by the assumption of the possibility of ad-atom formation and the growth of the metal phase layer in the deposition process on an indifferent solid electrode.

Chronopotentiometric deposition and stripping of silver, lead and copper at platinum electrodes

The effect of pre-treatment (pre-oxidation, pre-plating, or platinization) of a platinum electrode on the chronopotentiometric deposition and stripping of silver, lead and copper in various media is considered. Depositions were found to occur less reversibly at a pre-oxidized electrode. Evidence for retention of some deposited metal, even at potentials considerably more positive than the reversible stripping potential is presented and possible mechanisms for this retention are suggested.