Fullerene-based anodic stripping voltammetry for simultaneous determination of Hg(II), Cu(II), Pb(II) and Cd(II) in foodstuff

Various carbon nanomaterials for use in anodic stripping voltammetric analysis of Hg(II), Cu(II), Pb(II) and Cd(II) are screened. Graphene, carbon nanotubes, carbon nanofibers and fullerene (C₆₀), dispersed in chitosan (Chit) aqueous solution, are used to modify a glassy carbon electrode (GCE). The fullerene-chitosan modified GCE (C₆₀-Chit/GCE) displays superior performance in terms of simultaneous determination of the above ions. The electrodes and materials are characterized by electrochemical impedance spectroscopy, cyclic voltammetry, scanning electron microscopy, Raman spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The excellent performance of C₆₀-Chit/GCE is attributed to the good electrical conductivity, large surface area, strong adsorption affinity and unique crystalline structure of C₆₀. Using differential pulse anodic stripping voltammetry, the assay has the following features for Hg(II), Cu(II), Pb(II) and Cd(II), respectively: (a) Peak voltages of +0.14, ?0.11, ?0.58 and???0.82 V (vs SCE); (b) linear ranges extending from 0.01–6.0 μM, 0.05–6.0 μM, 0.005–6.0 μM and 0.5–9.0 μM; and (c), detection limits (3σ method) of 3 nM (0.6 ppb), 14 nM (0.9 ppb), 1 nM (0.2 ppb) and 21 nM (2.4 ppb). Moreover, the modified GCE is well reproducible and suitable for long-term usage. The method was successfully applied to the simultaneous determination of these ions in spiked foodstuff.

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Graphical abstract Compared with graphene, carbon nanotubes and carbon nanofibers, an electrode modified with fullerene in chitosan electrode displays superior performance for the simultaneous anodic stripping voltammetric detection of Hg(II), Cu(II), Pb(II) and Cd(II).

     

Analytical procedures for the simultaneous voltammetric determination of heavy metals in meals

An analytical procedure regarding the determination of copper(II), lead(II), cadmium(II), zinc(II) and antimony(III) in matrices involved in foods and food chain as wholemeal, wheat and maize meal is proposed. The digestion of each matrix was carried out using concentrated HCl suprapure at 130 °C for 3 h. Differential pulse anodic stripping voltammetry (DPASV) was employed for simultaneously determining all the elements, using a conventional three-electrode cell and 0.5 M HCl as supporting electrolyte. The analytical procedure has been verified on the reference standard materials Wholemeal BCR-CRM 189, Wheat Flour NIST-SRM 1567a and Rice Flour NIST-SRM 1568a. For all the elements in the certified matrix, the precision as repeatability, expressed as relative standard deviation (s_r), and the accuracy, expressed as relative error (e), were of the order of 3 to 6%. The limits of detection were in the range 0.009–0.096 μg/g.     

Catalytic determination of Pb(II) in the presence of Cu(II)

A kinetic method is presented to determine micro-molar amounts of Pb(II) from various river and wastewater samples, in the presence of trace copper. The procedure is based on the catalytic effect of both species on the oxidation of mercaptosuccinic acid by chromate in acidic media. The extent of the reaction is followed spectrophotometrically at 420 nm and pseudo-first-order rate coefficients of the rate-determining step are determined as a function of catalyst concentrations. The optimum operating conditions (ionic strength, temperature, and concentration of reagents) regarding sensitivity towards lead were established. Interference by several ionic species has been studied. The effect of Fe(III), the only severe interferent, is suppressed by complexation with 1,10-phenantroline. The bi-component calibration model employs an artificial neural network to compute the Pb(II) concentration from a k(obsd) value and the a priori-known Cu(II) concentration of the sample. Working concentration ranges are 20-2160 micro g L(-1) for Pb(II) and 80-650 micro g L(-1) for Cu(II), respectively. Detection limits are 20 micro g L(-1) Pb(II) and 80 micro g L(-1) Cu(II), respectively. The relative standard deviations (3 measurements) for four different testing points are lower than 2.5%. The method was applied to samples of river and wastewater of the mining region of Baia-Mare, Northern Romania. The results were compared to those obtained by an officially standardized AAS method. Good agreement was achieved. The method is inexpensive, fairly rapid, and sensitive. Its working range covers the exact range of concentrations usually encountered in the mentioned geographic area.     

Preparation of Cu (II) imprinted polymer electrode and its application for potentiometric and voltammetric determination of Cu (II)

The Cu (II) imprinted polymer glassy carbon electrode (GCE/Cu-IP) was prepared by electropolymerization of pyrrole at GCE in the presence of methyl red as a dopant and then imprinting by Cu²⁺ ions. This electrode was applied for potentiometric and voltammetric detection of Cu²⁺ ion. The potentiometric response of the electrode was linear within the Cu²⁺ concentration range of 3.9 × 10^?6 to 5.0 × 10^?2 M with a near-Nernstian slope of 29.0 mV decade^?1 and a detection limit of 5.0 × 10^?7 M. The electrode was also used for preconcentration anodic stripping voltammetry and results exhibited that peak currents for the incorporated copper species were dependent on the metal ion concentration in the range of 1.0 × 10^?8 to 1.0 × 10^?3 M and detection limit was 6.5 × 10^?9 M. Also the selectivity of the prepared electrode was investigated. The imprinted polymer electrode was used for the successful assay of copper in two standard reference material samples.     

Polarographic analytical determination of Hg(II), Cu(II), Cd(II), As(III), Sb(III), Ti(IV) and U(VI) in the presence of Fe(III)

The analytical determination of Hg(II), Cu(II), Cd(II), As(III), Sb(III), Ti(IV) and U(VI) in the presence of Fe(III) and 1 M H₂SO₄ are investigated using the polarographic technique. The wave corresponding to the reduction of Fe(III) to Fe(II) was found to be completely suppressed by the addition of 1% pyrogallol. Thus, different mixtures of these elements, viz. Hg(II), Cu(II), Cd(II), As(III) and Fe(III)-mixture (A), Cu(II), Cd(II), Sb(III), As(III) and Fe(III)-mixture (B), and Cu(II), Cd(II), Ti(IV), U(VI) and Fe(III)-mixture (C), were quantitatively determined using 1% pyrogallol and 1 M H₂SO₄ as supporting electrolyte. The i₁/c results give excellent correlations in each case, as indicated from the results of leastsquares regression analysis.     

Hg(II) immobilized MWCNT graphite electrode for the anodic stripping voltammetric determination of lead and cadmium

The preparation of Hg(II)-modified multi walled carbon nanotube (MWCNT) by reaction of oxidized MWCNT with aqueous HgCl₂ was carried out. The Hg(II)-modified multi walled carbon nanotube (Hg(II)/MWCNT) dispersed in Nafion solution was used to coat the polished graphite electrode surface. The Hg(II)/MWCNT modified graphite electrode was held at a cathodic potential (−1.0 V) to reduce the coordinated Hg(II) to Hg forming nanodroplets of Hg. The modified electrode was characterized by FESEM/EDAX which provided useful insights on the morphology of the electrode. The SEM images showed droplets of Hg in the size of around 260 nm uniformly distributed on the MWCNT. Differential pulse anodic stripping voltammetry (DPASV) and electrochemical impedance spectroscopy were used to study the Hg(II) binding with MWCNT. Differential pulse anodic stripping voltammetry of ppb levels of cadmium and lead using the modified electrode yielded well-defined peaks with low background current under a short deposition time. Detection limit of 0.94 and 1.8 ng L⁻¹ were obtained following a 3 min deposition for Pb(II) and Cd(II), respectively. Various experimental parameters were characterized and optimized. High reproducibility was observed from the RSD values for 20 repetitive measurements of Pb(II) and Cd(II) (1.7 and 1.9%, respectively). The determination of Pb(II) and Cd(II) in tap water and Pb(II) in human hair samples was carried out. The above method of fabrication of Hg(II)/MWCNT modified graphite electrode clearly suggests a safe route for preparing Hg immobilized electrode for stripping analysis.     

A screen-printed carbon electrode modified with a bismuth film and gold nanoparticles for simultaneous stripping voltammetric determination of Zn(II), Pb(II) and Cu(II)

The authors report on a disposable sensor for the differential pulse anodic stripping voltammetric (DPASV) determination of the ions Zn(II), Pb(II) and Cu(II). Simultaneous detection is accomplished by using a screen-printed carbon electrode (SPCE) co-modified with an in-situ plated bismuth (Bi)) film and gold nanoparticles (AuNPs). The synergistic effect of the Bi film, and the large surface and good electrical conductivity of the AuNPs strongly assist in the co-deposition of the three ions. Four well-defined and fully separated anodic stripping peaks, at 540 mV for Zn(II), 50 mV for Pb(II), 140 mV for Bi(III) and 295 mV for Cu(II), all vs. Ag/AgCl, can be seen. The modified SPCE was characterized by scanning electron microscopy, X-ray diffraction, cyclic voltammetry and electrochemical impedance spectroscopy. Under the optimized conditions, the sensor has a good response to these ions. The detection limits (at an S/N ratio of 3) are 50 ng·L^?1 for Zn(II), 20 ng·L^?1 for Pb(II), and 30 ng·L^?1 for Cu(II). The method was applied to the determination of the 3 ions in spiked lake water samples.

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Graphical abstract Schematic of screen-printed carbon electrode (SPCE) co-modified with a bismuth film and gold nanoparticles for electrochemical simultaneous determination of Zn(II), Pb(II) and Cu(II) by differential pulse anodic stripping voltammetric (DPASV).

     

New voltammetric procedure for the simultaneous determination of copper and mercury in environmental samples

Summary A new voltammetric procedure for the simultaneous determination of Cu and Hg down to the ng/l-range in environmental samples is described. Differential pulse anodic stripping voltammetry (DPASV) at a gold electrode is applied. There are two versions. For Hg-levels typically below 100 ng/l in presence of substantially higher Cu-concentrations (300 ng/l or more), e.g. in sea water, Hg has to be determined by the subtractive mode of DPASV at a twin gold electrode and programmed polarisation has to be applied during the cathodic deposition stage, while the usually higher Cu-levels can be determined by common DPASV at a normal gold electrode. For Hglevels above 100 ng/l the determination of Hg and Cu can be performed in the same run by common DPASV at a normal gold electrode. The application of the gold electrode always requires medium exchange to 0.1 M HClO₄ plus 2.5×10^–3 M HCl subsequent to the cathodic accumulation stage before stripping. The method has been successfully applied to natural waters and wine. The necessary sample pretreatment remains simple and consists just in UV-irradiation to release the trace metal amount bound to dissolved organic matter, which is performed with samples from natural waters after prior 0.45 -filtration to separate from suspended particulate material.

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Neues voltammetrisches Verfahren zur simultanen Bestimmung von Kupfer und Quecksilber in Umweltmaterial

Zusammenfassung Als Bestimmungsverfahren werden zwei Versionen der differentiellen Pulsinversvoltammetrie (DPASV) an der Goldelektrode eingesetzt. Bei Quecksilbergehalten typisch unter 100 ng/l und gleichzeitiger Anwesenheit höherer Kupferkonzentrationen (300 ng/l), wie z.B. im Meerwasser, muß Hg mit der subtraktiven DPASV an einer Zwillingselektrode aus Gold bestimmt werden und während des kathodischen Anreicherungsschrittes erfolgt programmierte Polarisation der Goldelektrode. Hingegen können die gewöhnlich höheren Cu-Gehalte mit der üblichen konventionellen DPASV an einer normalen Goldelektrode bestimmt werden. Bei Hg-Gehalten oberhalb 100 ng/l kann die Bestimmung von Hg und Cu in einem voltammetrischen Arbeitsgang mit der konventionellen üblichen DPASV an einer normalen Goldelektrode erfolgen. Die Verwendung der Goldelektrode verlangt immer Wechsel des Mediums zu 0,1 M HClO₄ plus 2,5 ×10^–3 M HCl nach der kathodischen Anreicherung vor der stripping-Phase. Die Methode hat erfolgreiche Anwendung bei der Untersuchung natürlicher Gewässer und von Wein gefunden. Die erforderliche Probenvorbereitung bleibt einfach und besteht in einer UVBestrahlung, um den durch gelöste organische Materie gebundenen Spurenmetallanteil zu mobilisieren. Bei Proben aus natürlichen Gewässern erfolgt vorher eine 0,45 -Filtration zur Abtrennung von Schwebstoffen.

     

Self-assembled monolayers of 2-mercaptobenzimidazole on gold: stripping voltammetric determination of Hg(II)

Monomolecular level modification of electrode surfaces through a self-assembly approach is, of late, gaining importance in view of its many functional applications in areas such as molecular electronics, molecular recognition, electron transfer studies and electroanalysis. Self-assembled monolayer (SAM) modification of a gold electrode with 2-mercaptobenzimidazole (MBI) has been achieved. On this modified electrode, anodic stripping voltammetric determination of mercury at ppm/sub-ppm level concentrations has been successfully attempted. Pre-concentration, prior to stripping, has been effected through a non-electrolytic process involving chemical interactions between MBI and Hg(II). The results are described and discussed with a plausible scheme.     

A novel 1,10-phenanthroline-sensitive membrane sensor for potentiometric determination of Hg(II) and Cu(II)cations

Preparation, characterization, and applications of a 1,10-phenanthrolinium cation (phenH(+))-sensitive potentiometric sensor are described. The sensor incorporates a liquid polymeric membrane consisting of phenH-tetraphenylborate, nitrophenyloctyl ether, and poly(vinyl chloride) as ion exchanger, plasticizer, and polymeric support, respectively. The sensor exhibits a fast and Nernstian response to phenH(+) over the concentration range of 6 x 10(-6)-2 x 10(-4) M with a monovalent cationic slope of 58.0+/-0.5 mV/log[phenH(+)] in acetate buffer of pH 4.2. The sensor is successfully applied to the monitoring of the potentiometric titration of Hg(II) and Cu(II) ions with phen solution in the presence of citrate and acetate buffers of pH 4.2, respectively. Sharp inflection breaks (90-180 mV) at 1:1 (metal:phen reaction) are obtained in the presence of chloride and thiocyanate background. This stoichiometry is explained by the formation of insoluble [HgCl(2)(phen)], [Hg(SCN)(2)(phen)], and [Cu(SCN)(2)(phen)] complexes. Optimization of each titration and the effect of foreign ions are evaluated. The method offers the advantages of adequate sensitivity, accuracy, and selectivity for the determination of mercury and copper in pharmaceutical, rock, and tea samples. The results are in good agreement with those obtained using the standard atomic absorption spectrometric and United States Pharmacopeial methods.     

Optimization of the simultaneous batch determinations of Bi(III), Hg(II) and Cu(II) at an epoxy-graphite electrode bulk modified with 2-mercaptobenzothiazole

An epoxy-graphite tube composite electrode bulk modified with 2-mercaptobenzothiazole was investigated for the simultaneous, batch determinations of Bi(III), Hg(II) and Cu(II) by differential-pulse anodic stripping voltammetry after open circuit preconcentration of the three metal ions. Systematic optimization was studied with respect to resolution and sensitivities of the differential-pulse peaks. The resolution between peaks was quantified and employed in a window diagram approach to choose the best conditions. The developed method gave detection limits of 4.2 x 10(-9), 3.6 x 10(-9) and 9.5 x 10(-8) M for Hg(II), Bi(III) and Cu(II), respectively (S/N = 3; 3 min preconcentration). The conditions whereby simultaneous determinations could be performed in the absence of cross-interferences of the analytes were also examined. Additional selected substances in the sample background were also studied for possible interferences. The developed method was applied to the simultaneous, batch determinations of Bi(III), Hg(II) and Cu(II) in a standard sample and a human hair sample.     

Analytical procedure for the simultaneous voltammetric determination of trace metals in food and environmental matrices. Critical comparison with atomic absorption spectroscopic measurements

An analytical procedure fit for the simultaneous determination of copper (II), chromium(VI), thallium(I), lead(II), tin(II), antimony(III), and zinc(II) by square wave anodic stripping voltammetry (SWASV) in three interdependent environmental matrices involved in foods and food chain as meals, cereal plants and soils is described. The digestion of each matrix was carried out using a concentrated HCl-HNO3-H2SO4 (meals and cereal plants) and HCl-HNO3 (soils) acidic attack mixtures. 0.1 mol/L dibasic ammonium citrate pH 8.5 was employed as the supporting electrolyte. The voltammetric measurements were carried out using, as working electrode, a stationary hanging mercury drop electrode (HMDE) and a platinum electrode and an Ag/AgCl/KClsat electrode as auxiliary and reference electrodes, respectively. The analytical procedure was verified by the analyses of the standard reference materials: Wholemeal BCR-CRM 189, Tomato Leaves NIST-SRM 1573a and Montana Soil Moderately Elevated Traces NIST-SRM 2711. For all the elements in the certified matrix, the precision as repeatability, expressed as relative standard deviation (Sr %) was lower than 5%. The accuracy, expressed as percentage relative error (e %) was of the order of 3-7%, while the detection limits were in the range 0.015-0.103 microg/g. Once set up on the standard reference materials, the analytical procedure was transferred and applied to commercial meal samples, cereal plants and soils samples drawn in sites devoted to agricultural practice. A critical comparison with spectroscopic measurements is also discussed.     

A novel method for the simultaneous determination of Pb (II), Cd (II) and Zn (II) in environmental water samples

A novel UV-VIS spectrophotometric method was developed in this study by using solid phase extraction procedure for the simultaneous preconcentration, separation and determination of trace levels of Pb (II), Cd (II) and Zn (II) ions in various water samples by using Amberlite N,N-bis(salicylidene)cyclohexanediamine (SCHD) resin. This study presents the results of experimental procedures carried out like the adsorption of analytes to the resin, influences of some analytical parameters that effect the recovery such as pH, sample volume, sample flow rate, eluent type and concentration, eluent volume, eluent flow rate and the effects of alkaline metals, earth alkaline metals and some other transition metals. The analytes in the samples with the adjusted pH range of 4–7 were adsorbed on XAD-4-SCHD resin and eluted by using 1.0 mol L^?1 nitric acid. The amounts of ions were determined by using UV-VIS spectrometer. The limits of detection were 0.03, 0.07 and 0.05 µg mL^?1 for Pb (II), Cd (II) and Zn (II), respectively. The accuracy of the method was assured by the analysis of the certified standard water sample NW-TMDA-70.2 and the observed recoveries were above 93%. Different environmental water samples that contain trace amounts of Pb (II), Cd (II) and Zn (II) were analysed by using the method developed in this study. Same samples were also analysed by ICP-MS for comparison and almost the similar results were observed. The method developed in this study was successfully applied to the various environmental water samples to determine the trace levels of Pb (II), Cd (II) and Zn (II) ions.     

Square wave voltammetric determination of Hg(II) using thiol functionalized chitosan-multiwalled carbon nanotubes nanocomposite film electrode

Covalent tethering of cysteamine to chitosan using glutaraldehyde yields thiol-functionalized chitosan (CS-SH). It was cast on a glassy carbon electrode which is found to be very stable in acidic solutions and to possess a strong affinity for Hg(II) ions as confirmed by quartz crystal microbalance measurements. A glassy carbon electrode modified with a nanocomposite made from CS-SH and multiwalled carbon nanotubes was applied for square wave voltammetric determination of Hg(II). The procedure comprises the steps of (a) chemical accumulation of Hg(II) under open-circuit condition and (b) electrochemical determination of Hg(II). Linear responses are obtained in the range from 10 to 140 nM, with a limit of detection of 3 nM (S/N?=?3) under optimized conditions. The electrode was applied to the determination of Hg(II) in water samples with satisfactory recoveries.     

H-point standard addition method for simultaneous determination of Fe(II), Co(II) and Cu(II) in micellar media with simultaneous addition of three analytes

H-point standard addition method, HPSAM, with simultaneous addition of three analytes is proposed for the resolution of ternary mixtures. It is a modification of the previously described H-point standard addition method that permits the resolution of three species from a unique calibration set by making the simultaneous addition of the three analytes. The method calculates the analyte concentration from spectral data at two wavelengths where the two species selected as interferents present the same absorbance relationship. These wavelength pairs are easily found, and can be selected to give the most precise results. Diethyldithiocarbomate (DDC) in a cationic micellar solution of cetyltrimethylammonium bromide (CTAB) was used for determination of Fe(II), Co(II) and Cu(II) at pH 5.50. The results showed that simultaneous determination of Fe(II), Co(II) and Cu(II) could be preformed in the range of 0.0–6.0, 0.0–8.0 and 0.0–12.0 μg ml⁻¹, respectively. The proposed method was successfully applied to the simultaneous determination of Fe(II), Co(II) and Cu(II) in several synthetic mixtures containing different concentration of Fe(II), Co(II) and Cu(II).     

Dual-wavelength spectrophotometric determination of traces of mercury(II) with solubilized dithizone: An approach to simplified analytical procedures for environmental pollutants

A simple spectrophotometric procedure is described for the determination of traces of mercury, with solubilized copper(II) dithizonate. Sample water containing 0.05–0.25 μg of mercury(II) is mixed with an aqueous solution of copper dithizonate containing Triton X-100 at pH 1 (H₂SO₄ ). After 5 min, dual-wavelength photometry is used to measure the difference in absorbances at 507 and 493 nm, which is proportional to the mercury concentration. The advantages are that no reagent blank is necessary and the equipment is simple. Few cations interfere; silver(I) and iron(III) can be masked by chloride and fluoride, respectively.     

Application of lead film electrode for simultaneous adsorptive stripping voltammetric determination of Ni(II) and Co(II) as their nioxime complexes

An adsorptive stripping voltammetric (AdSV) procedure for simultaneous determination of Ni(II) and Co(II) in the presence of nioxime as a complexing agent at an in situ plated lead film electrode was described. The Co(II) signal was enhanced by exploitation of the catalytic process in the presence of nitrite. Ni(II) and Co(II) signals are better separated than in the case of bismuth film electrodes. Calibration graphs for an accumulation time of 120 s are linear from 1 × 10⁻⁹ to 1 × 10⁻⁷ mol L⁻¹ and from 1 × 10⁻¹⁰ to 5 × 10⁻⁹ mol L⁻¹ for Ni(II) and Co(II), respectively. The proposed procedure was applied for Ni(II) and Co(II) determination in water certified reference materials.     

A rapid high-performance analytical procedure with simultaneous voltammetric determination of toxic trace metals in urine

For the monitoring of toxic trace metals in urine a new high-performance trace analytical procedure with simultaneous voltammetric determination is presented. Particular emphasis has been placed on minimizing contamination by reducing the urine sample volume to 1 ml and consequently limiting the needed amount of HNO(3)/HClO(4) and the duration (<20 min) of the wet digestion stage. The procedure consists of three stages. First 20 urine samples (1 ml each) are simultaneously freeze-dried overnight. They then require only a short wet digestion (HClO(4)/HNO(3) 2:1, 20 min, 210 degrees ). They are then adjusted to pH 4.5 with acetate buffer and the trace metals are determined simultaneously by differential pulse anodic-stripping voltammetry at the mercury film electrode, the quartz digestion vessel being used as the voltammetric cell. If precipitates occur in the acidified samples, their trace metal content can be determined in the same manner, avoiding the low results commonly obtained by other methods. The procedure has high sensitivity with fair to good precision, covers a determination range from the sub-mug/l. to the medium mug/l. level and lends itself to automation. It is cheaper and more accurate than atomic absorption. Thus the procedure provides important potentialities for surveillance of occupationally exposed persons as well as for extended ecotoxicological baseline studies in man and cattle.     

Bismuth-dispersed xerogel-based composite films for trace Pb(II) and Cd(II) voltammetric determination

We report for the first time the synthesis of bismuth-modified (3-mercaptopropyl) trimethoxysilane (MPTMS) and its application for the determination of lead and cadmium by anodic stripping voltammetry. Xerogels made from bismuth-modified MPTMS and mixtures of it with tetraethoxysilane, under basic conditions (NH₃·H₂O), were characterized with scanning electron microscopy, energy dispersive spectroscopy, infrared spectroscopy and electrochemical methods. Bismuth-modified xerogels were mixed with 1.5% (v/v) Nafion in ethanol and applied on glassy carbon electrodes. During the electrolytic reductive deposition step, the bismuth compound on the electrode surface was reduced to metallic bismuth. The target metal cations were simultaneously reduced to the respective metals and were preconcentrated on the electrode surface by forming an alloy with bismuth. Then, an anodic voltammetric scan was applied in which the metals were oxidized and stripped back into the solution; the voltammogram was recorded and the stripping peak heights were related to the concentration of Cd(II) and Pb(II) ions in the sample. Various key parameters were investigated in detail and optimized. The effect of potential interferences was also examined. Under optimum conditions and for preconcentration period of 4 min, the 3σ limit of detection was 1.3 μg L⁻¹ for Pb(II) and 0.37 μg L⁻¹ for Cd(II), while the reproducibility of the method was 4.2% for lead (n = 5, 10.36 μg L⁻¹ Pb(II)) and 3.9% for cadmium (n = 5, 5.62 μg L⁻¹ Cd(II)). Finally, the sensors were applied to the determination of Cd(II) and Pb(II) ions in water samples.     

Selenium-coated carbon electrode for anodic stripping voltammetric determination of copper(II)

We describe a new and promising type of selenium film electrode for anodic stripping voltammetry. This method is based on formation of copper selenide onto an in-situ formed selenium-film carbon electrode, this followed by Osteryoung square-wave anodic stripping voltammetry. Copper(II) is also in-situ electroplated in a test solution containing 0.01 mol L^-1 hydrochloric acid, 0.05 mol L^?1 potassium chloride and 500 µg L^?1 Se(IV) at a deposition potential of ?300 mV. The well-defined anodic peak current observed at about 200 mV is directly proportional to the Cu(II) concentration over the range from 1.0 to 100 µg L^?1 under the optimized conditions. The detection limit (three sigma level) is 0.2 µg L^?1 Cu(II) at 180 s deposition time. Relatively less interferences are shown from most of metal ions except for antimony(III). The method can be applied to analyses of river water and oyster tissue with good accuracy.