Direct and simultaneous determinations of Zn,Cd, Pb,Cu, Sb and Bi dissolved in sea water by differential pulse anodic stripping voltammetry with a hanging mercury drop electrode

Differential pulse anodic stripping voltammetry with a hanging mercury drop electrode is used for the direct and simultaneous determination of Zn, Cd, Pb, Cu, Sb and Bi at their natural levels in sea water after adjustment to pH 1 and to a 2 M chloride concentration. The optimal instrumental parameters are described. With a plating time of 60 min, the detection limits are about 0.1 ppb for Zn and Cu, 0.01 ppb for Cd and Pb, and 0.05 ppb for Sb and Bi. Relative standard deviations are about 10—15%. Simultaneous determinations of the six metals take about 2 h.     

The cathodic stripping voltammetry of certain thiols in acetate medium

The cathodic stripping voltammetry of six thiols by deposition at a hanging mercury drop electrode (+0.05 V vs. SCE) from acetate-buffered solution (pH 4.76) and scanning to —0.8 V is described. Peak potentials are reported. The peak height—concentration relationships are reasonably linear in the range 0.4–1.2 μM. The compounds tested are 2-mercaptopyridine, 2-mercapto-3-pyridinol, 2-mercaptopyridine-N-oxide, mercaptosuccinic acid, 2-mercaptopyrimidine and cysteine hydrochloride.     

Voltammetric Quantification of Zn and Cu,Together with Hg and Pb,Based on a Gold Microwire Electrode,in a Wider Spectrum of Surface Waters

The simultaneous determination of Zn and Cu by anodic stripping voltammetry (ASV) is prone to errors due to the formation of Cu‐Zn intermetallic compounds. The main aim of this work was to study the possibility of simultaneous determination of Zn and Cu, together with Hg and Pb, using a mercury‐free solid gold microwire electrode. The multi‐element detection was carried out by differential pulse anodic stripping voltammetry (DPASV), in a chloride medium (0.5 M NaCl) under moderate acid conditions (HCl 1.0 mM) in the presence of oxygen, where the gold microwire electrode was used as stationary or vibrating working electrode during the deposition step. Under these conditions, no formation of Cu‐Zn intermetallic compounds were found for concentrations usually determined in surface waters. In addition, quantification of Zn and Cu, together with Hg and Pb, can be performed in a wide range of concentrations (about two orders of magnitude) using the same sample, in a very short period of time. The detection limits for Cu, Hg, Pb and Zn, using a vibrating electrode and 30 s of deposition time, were 0.2 µg L^?1 for Hg, 0.3 µg L^?1 for Pb and 0.4 µg L^?1 for Zn and Cu, respectively. The proposed DPASV methods were successfully applied to the determination of Cu, Hg, Pb, and Zn in a certified reference fresh water, river, tap and coastal sea waters. These results proved the applicability and versatility of the proposed methods for the analysis of different water matrices and showed that a gold microwire electrode is a suitable choice to determine simultaneously Zn and Cu.     

In situ electrodeposition for the determination of lead and cadmium in sea water

Electrodeposition techniques for the direct determination of lead and cadmium in sea water at the natural pH and in the presence of dissolved oxygen are examined. Anodic stripping voltammetry, at either the hanging mercury drop electrode or glassy carbon thin film electrode, is suitable for the determination of labile lead and cadmium. The presence of dissolved oxygen increases the height of the lead wave with a shift to more negative potentials. A more versatile technique is in situ deposition of labile metals on a mercury-coated graphite tube electrode. The mercury film, deposited in the laboratory, is stable on the dried tubes which are used later for field electrodeposition. The deposited metals are determined by electrothermal atomic absorption spectrometry.     

Simultaneous Determination of Copper(II), Lead(II) and Zinc(II) at Bismuth Film Electrode by Multivariate Calibration

In this work, simultaneous determination of Cu(II), Pb(II) and Zn(II) ions at low concentration levels (ppb) by square wave anodic stripping voltammetry on a Bi(III) film electrode plated in situ at a glassy carbon electrode (GCE) is described. A chemometric approach was used to overcome the overlapping peaks of Cu(II) and Bi(III), the competition of the electrodeposited Cu and Bi for the surface of the GCE and the formation of Cu‐Zn intermetallic compounds. The construction of the multivariate calibration models, based on partial least squares regression, allowed the simultaneous determination of Cu (in the concentration range 8.0 to 20.1 ppb), Pb (2.0 to 30.0 ppb) and Zn (29.7 to 90.4 ppb) with most of the prediction errors obtained in the external validation set for the three models lower than 16, 11 and 26 %, respectively. Finally, this method was used for the determination of these trace metal ions in surface river water samples with satisfactory results [errors below 10, 5 and 32 % for Cu(II), Pb(II) and Zn(II), respectively].     

Determination of heavy metals in real samples by anodic stripping voltammetry with mercury microelectrodes : Part 2. Application to Rain and Sea Waters

Differential-pulse anodic stripping voltammetry at a mercury microelectrode is applied to determine labile and total zinc, cadmium, lead and copper in samples of rain and sea water. The low ohmic drop associated with microelectrodes permits reliable measurements in rain water without addition of supporting electrolyte. The values found in a typical sample were 0.95 μg l^?1 Cu, 0.38 μg l^?1 Pb, 0.01 μg l^?1 Cd and 0.95 μg l^?1 Zn, with relative standard deviations in the range 4–18%. The small effects of organic matter at microelectrodes, compared with those at a hanging mercury drop electrode, allow sensitive and reliable measurements of labile metals in surface sea water. Total metal concentrations are determined after acidification to pH 1.5 with hydrochloric acid. The results are compared with those obtained with atomic absorption spectrometry and with differential-pulse anodic stripping voltammetry at conventional mercury electrodes. Satisfactory results were obtained for a reference sea water.     

Dithlzone extraction and flame atomic absorption spectrometry for the determination of cadmium,zinc, lead,copper, nickel,cobalt and silver in sea water and biological tissues

The method previously described for the determination of Cd, Zn, Cu, Ni and Co in sediments has been adapted for the determination of these metals, and lead and silver in sea water and biological tissues. For sea water the only treatment preceding extraction is pH adjustment; biological tissues are digested in nitric and perchloric acids and the residue taken up in dilute hydrochloric acid prior to pH adjustment and extraction. The method is sufficiently sensitive to allow Cd, Zn, Cu and Ni to be determined in all sea waters, Co and Ag in coastal waters, but Pb only in polluted water.     

Simultaneous determination of Cd, Pb, Cu, Sb, Bi, Se, Zn, Mn, Ni, Co and Fe in water samples by differential pulse stripping voltammetry at a hanging mercury drop electrode

A highly sensitive and selective voltammetric procedure is described for the simultaneous determination of eleven elements (Cd, Pb, Cu, Sb, Bi, Se, Zn, Mn, Ni, Co and Fe) in water samples. Firstly, differential pulse anodic stripping voltammetry (DPASV) with a hanging mercury drop electrode (HMDE) is used for the direct simultaneous determination of Cd, Pb, Cu, Sb and Bi in 0.1 M HCI solution (pH = 1) containing 2 M NaCl. Then, differential pulse cathodic stripping voltammetry (DPCSV) is used for the determination of Se in the same solution. Zn is subsequently determined by DPASV after raising the pH of the same solution to pH 4. Next, the pH of the medium is raised to pH 8.5 by adding NH3/NH4Cl buffer solution for the determination of Mn by DPASV. Ni and Co are determined in the same solution by differential pulse adsorptive stripping voltammetry (DPAdSV) after adding DMG (1 x 10(-4) M). Finally, 1 x 10(-5) M 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) is added to the solution for the determination of Fe by DPAdSV. The optimal conditions are described. Relative standard deviations and relative errors are calculated for the eleven elements at three different concentration levels. The lower detection limits for the investigated elements range from 1.11 x 10(-10) to 1.05 x 10(-9)M, depending on the element determined. The proposed analysis scheme was applied for the determination of these eleven elements in some ground water samples.     

An evaluation of differential pulse anodic stripping voltammetry at a rotating glassy carbon electrode for the determination of cadmium,copper, lead and zinc in antarctic snow samples

A procedure is described for the determination without preconcentration of Cd, Cu, Pb and Zn in Antarctic snow, based on differential pulse anodic stripping voltammetry at a rotating glassy carbon electrode with in situ mercury plating. Thirty four surface snow samples from Adelaide Island in the Antarctic Peninsula demonstrate the scope of this method, and allow an assessment of local heavy metal sources such as the rock, the sea, and a manned base. The zinc data are affected by container contamination, but concentrations as low as 0.005, <0.02 and 0.05 ng g^-1 were measured for Cd, Cu and Pb, respectively.     

Anodic stripping voltammetry with the florence mercury film electrode. determination of copper,lead and cadmium in sea water

The use of the rotating glassy carbon electrode mercury plated in situ for anodic stripping voltammetry has been investigated. The choice of electrode material is discussed. The effect of instrumental parameters on the stripping response for copper, lead and cadmium in sea water is studied, the results being in accordance with the theory of thin film electrodes. The variation in the observed sensitivity for the three metals in sea water is discussed in terms of complex-forming ligands. Lastly the performance of the film electrode is compared to that of the hanging mercury drop electrode.     

Renewable silver amalgam film electrodes in electrochemical stripping analysis—a review

The success of a voltammetric sensing procedure depends mainly on the proper choice of the working electrode. This is because its ability to accumulate the analyte determines the sensitivity of the method. The main criterion of the selection of the proper working electrode is the available potential window. A variety of conductive materials have been used for the preparation of working electrodes. Of these, two kinds of mercury electrodes—hanging mercury drop and film—were used because of their excellent voltammetric performance and, in particular, their high overpotential of hydrogen reduction. The significant drawbacks of mercury electrodes, however, are the toxicity of the material and the instability of liquid mercury films. To overcome these disadvantages, less toxic mercury-containing materials have been used, such as amalgams and amalgam film electrodes. This group includes renewable silver amalgam film electrodes used for electrochemical stripping sensing purposes. These electrodes have successfully been applied for anodic, adsorptive, cathodic, catalytic voltammetric, and potentiometric stripping determination of trace amounts of inorganic cations and organic compounds in various natural matrices. In this review, the electrode design, characteristics, and application of two kinds of renewable silver amalgam film electrodes are discussed in detail.     

High-precision analysis of nuclear materials by constant-current coulometry : Part II. Determination of thorium

A constant-current coulometric method is described for the precise determination of thorium by titration with EDTA, elcctrogenerated from its mercury complex in acetate-buffered solution at pH 4.5. With polarised mercury electrodes for end-point detection, relative standard deviations of 0.02 and 0.3% for 30 mg and 30 μg respectively were obtained; the method was applied to the analysis of zone-refined thorium of high purity.     

Intermetallic compounds and the determination of copper and zinc by anodic stripping voltammetry

The intermetallic CuZn compounds produced during the simultaneous deposition of copper and zinc at a preformed mercury film electrode were studied. Over a wide range of metal concentration ratios, the real concentrations of metals in the amalgam were calculated from the peak areas obtained by anodic stripping voltammetry. The results indicate the formation of CuZn (insoluble) and CuZn2 (soluble) compounds with K_so=5×10^?4 and β₂=100, respectively. The electrodeposition potential of ?0.85 V vs. SCE for the reduction of copper in presence of zinc is confirmed as correct.     

Determination of traces of metals by anodic stripping voltammetry at a rotating glassy carbon ring—disc electrode: Part 1. Method and instrumentation with evaluation of some parameters

The equipment and procedure are described for the determination without preconcentration of several heavy metals based on d.c. anodic stripping voltammetry at a rotating ring—disc glassy carbon electrode with in situ mercury plating. During stripping of the metals deposited on the disc, the current from the reduction of the ions collected at the ring is measured. Some parameters (scan rate, thickness of the mercury film, electrode rotation and deposition time) influencing the ring collection peak current are examined experimentally. The results are compared with the theoretical considerations given by de Vries and van Dalen for anodic stripping voltammetry on a stationary mercury film electrode and by Bakanov et al. for a rotating mercury film electrode.     

Trace amounts determination of lead,zinc and copper by adsorptive stripping voltammetry in the presence of dopamine

A selective and sensitive method for simultaneous determination of lead, zinc and copper by adsorptive differential pulse cathodic stripping voltammetry is presented. The method is based on adsorptive accumulation of the complexes of Pb(II), Zn(II), and Cu(II) ions with dopamine onto hanging mercury drop electrode (HMDE), followed by reduction of adsorbed species by differential pulse cathodic stripping voltammetry. The effect of experimental parameters such as pH, dopamine concentration, accumulation time and potential and scan rate were examined. Under the optimized conditions, linear calibration curves were established for the concentration of Pb, Zn, and Cu in the ranges of 5–150, 5–250, and 1–150 ng/mL, respectively. Detection limits of 0.06, 0.25, and 0.04 ng/mL for Pb, Zn, and Cu were obtained. An application of the proposed method is reported for the determination of these elements in some real samples such as natural waters and alloys.     

Adsorption of Co, Ni, Cu, and Zn on hydrous manganese dioxide from complex electrolyte solutions resembling sea water in major ion content

Adsorption of Co, Ni, Cu, and Zn onto a poorly crystalline hydrous manganese dioxide (delta-MnO2) has been studied in complex electrolyte solutions such as (a) 0.5 M NaCl+0.054 M MgCl2, (b) 0.5 M NaCl+0.028 M Na2SO4, and (c) artificial sea water prepared according to the standard literature method. These three solutions allow us to identify the specific effect of major cations, major anions, and the mixture of major cations and anions (including carbonate and bicarbonate) that is present in real sea water. The adsorption isotherm in major ion sea water at pH 7.25 indicates that while Co and Zn exhibit increases in adsorption with increase in concentration, Ni shows relatively poor adsorption, reaching a plateau at 0.075 mM concentration. The three trace metals (Co, Ni, and Zn) show Langmuirian behavior for adsorption at low concentration. It is generally observed that the fractional adsorption vs pH curve shifts to higher pH either in the presence of 0.054 M MgCl2 or in sea water. In the presence of 0.028 M Na2SO4 the fractional adsorption vs pH curve remains almost unchanged with respect to a 0.5 M NaCl solution. The competitive adsorption of one trace metal in the presence of other three in major ion sea water indicates that this phenomenon is more predominant with Ni and Zn than with Co and Cu.     

Determination of selenium in sea water by adsorptive cathodic stripping voltammetry

A procedure is presented for determining Se(IV) and total dissolved Se in sea water using cathodic stripping voltammetry in the presence of added copper. Experiments using cyclic voltammetry indicate that the preconcentration step consists in adsorption of a Cu(I)₂Se complex species on the hanging mercury drop electrode. The optimized analytical conditions include a copper concentration of 40 μM and a solution pH of 1.6. Differential pulse modulation is used. Interference caused by organic surface-active substances present in natural waters in eliminated by UV photolysis of the sample. Cadmium interferes with the determination of Se only when present at a concentration 100 times higher than normal. UV photolysis at pH ≈ 8 is used to convert Se(VI), which is the electroactive species. The response is linear for Se concentrations between 0 and 200 nM. The limit of detection is 0.01 nM Se when a deposition time of 15 min is used.     

The effect of inorganic particulates on the ASV signals of Cd, Pb and Cu

The potential influence of inorganic particulates on the ASV response of < 100-microg/l. levels of Cd, Pb and Cu, at a thin film mercury electrode, was examined by adding various weights of the solids to the acetate background electrolyte solution. Materials added included the hydrous oxides of Mn(IV), FE(III) or Al(III), clay minerals (kaolinite, illite, montmorillonite) and some contaminated sediments. Abrasion of the mercury film was minimized by deaerating the turbid solutions before their transfer to the measuring cell. The hydrous oxides specifically sorbed all three metal ions, resulting in peak-size changes that varied in magnitude with pH. With the clays, only sorption of Pb by illite or montmorillonite was detected. The presence of the solids had little effect on the peak position or half-peak breadth of the Cd or Pb signals, but the Cu peak parameters changed, indicating some hydroxy-species formation at higher pH. Some contaminated sediment samples released a significant fraction of their total metal content into acetate buffer solutions. Shielding the mercury film with a semipermeable membrane had a similar effect to filtering the suspension before analysis, but diffusion equilibrium was only slowly achieved (> 12 hr).     

Direct zinc determination in commercial sulphuric acid by dpasv. Comparison of rotating disc and stationary graphite electrodes

A striking gas technique employed made a direct Zn determination possible at extremely low pH in commercial acid solutions when a stationary impregnated graphite-based mercury film electrode was used. The original Zn(II) concentrations were determined quantitatively by differential pulse anodic stripping voltammetry on 0.5M and 1M sulphuric acid solutions by standard addition and were found to be 2 x 10(-8)M and 4.1 x 10(-8)M, respectively. The influence of mercury ion concentration, pulse amplitude, potential step and pulse repetition time on analytical data was studied and optimized. A rotating disc graphite electrode was also used as a working electrode and was found unreliable for this purpose as hydrogen bubbles were not removed effectively and blocked the working electrode surface.     

Ethylenediamine in the voltammetric determination of copper in sea water at a rotating mercury film electrode

The use of ethylenediamine in the voltammetric study of copper in natural sea water was evaluated for applicability with rotating thin mercury film electrodes. It was shown that this method increases the analytical sensitivity for copper at such electrodes by at least a factor of 4, and improves the detection of pH 8 labile copper.