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Sensitive Anodic Stripping Voltammetric Copper Ions Determination Performed in Double Deposition and Double Stripping Steps System for Real Water Samples Analysis
Abstract
The article reports on utilization of double deposition and stripping steps for increasing sensitivity of Cu(II) determination by anodic stripping voltammetry (ASV) at two lead film working electrodes. A significant preconcentration of copper was achieved thanks to utilization of a simple design of four electrodes system that gives possibility to perform one measurement cycle consisting of two deposition and two stripping steps. Due to the fact that deposition step is doubled, the concentration of Pb(II) needed to lead film electrodes formation was significantly reduced as compared to traditional procedures using three electrodes system. The analytical procedure of Cu(II) determination was optimized. The experimental factors: supporting electrolyte's pH and its concentration, lead ions concentration, potential and time of deposition at both working electrodes were studied. The Cu(II) peak current was linearly dependent on its concentration from 5×10−10 to 2×10−8 mol L−1 (deposition time of 270 and 160 s at the first and the second working electrode, respectively). The obtained detection limit for copper ions determination was 2.1×10−10 mol L−1. The described procedure was validated by analysis of two water certified reference materials. The described procedure was also utilized for real water sample analysis.
The article reviews an application of double deposition/accumulation and stripping steps as a new and beneficial manner of decreasing a detection limit and/or interferences elimination in stripping voltammetric determination of inorganic ions: Pb(II), Cd(II), Tl(I), U(VI), Au(III), As(III), Se(IV), In(III), Co(II), Cu(II), Bi(III) and Ga(III). A simple design of four‐electrodes system, containing two working electrodes differing in their surface area, allows for conducting two preconcentration and two stripping steps in one measurement cycle and in one voltammetric cell. Considerable analytes preconcentration and, consequently, an increase of sensitivity of determinations was obtained by conducting the first stripping step in a small volume of a solution near the microelectrode surface. An appropriate selection of the conditions of the first deposition/accumulation and the first stripping steps allowed for a minimization/elimination of interference effects. The proposed procedures allows for ultra‐trace levels determinations of mentioned inorganic ions (often impossible to determine by means of traditional three‐electrodes systems) without additional preconcentration outside the electrochemical cell and with the use of mercury‐free electrodes.
An anodic stripping voltammetric procedure for the determination of bismuth in the presence of excess of Cu2+ ions at two ex situ plated gold film electrodes was described. The procedure is based on utilization of two deposition and two stripping steps system. The presented procedure ensures increasing the sensitivity of Bi3+ determination and minimization of interferences related to peaks’ overlapping. The calibration graph for bismuth determination was linear from 2.5 × 10‐9 to 2 × 10‐8 mol L‐1 for deposition time of 300 s at both working electrodes while detection limit was 8.2 × 10‐10 mol L‐1.
A procedure for the determination of In(III) by anodic stripping voltammetry following double deposition and stripping steps was described. Two environmentally friendly electrodes with different surface areas-glassy carbon macroelectrode and an ensemble of carbon composite microelectrodes-modified with bismuth films were used for the measurements. Parameters affected In(III) determination were optimized. Under optimized conditions the calibration graph was linear from 5 × 10⁻¹⁰ to 2 × 10⁻⁸ mol L⁻¹ following deposition time of 300 s at both working electrodes. The application of double deposition and stripping steps led to a very low detection limit of indium determination of 1.5 × 10⁻¹⁰ mol L⁻¹. Possible interferences from contaminant metal ions were studied and the procedure of elimination of Cd(II) effect on In(III) signal was proposed. The analysis of natural water sample was successfully performed with the use of the presented methodology.
Copper(II) was selectively accumulated, at open circuit, on a carbon paste electrode incorporating N-phenylcinnamohydroxamic acid. The ensuing measurements were carried out by differential pulse anodic stripping voltammetry. Factors affecting the accumulation, reduction, and stripping steps were investigated and a procedure was developed. Two linear ranges were obtained in the concentration ranges 1.00×10−8 –1.00×10−6 M Cu(II) with 3 min preconcentration time and 1 min reduction time and 1.00×10−9–1.00×10−8 M Cu(II) with 10 min preconcentration time and 2 min reduction time. The detection limit was found to be 5.00×10−10 M with 10 min accumulation and 2 min reduction time. For six successive determinations of 1.00×10−8 and 5.00×10−7 M Cu(II), relative standard deviations of 9.4 and 8.7%, respectively, were obtained. The modified electrode preferentially accumulates copper from the solution, while most of the metal ions do not interfere with the determination. The developed method was applied to copper determination in potable water and in commercial lithium chloride.
The feasibility of fabricating copper-sensitive chemically modified electrodes (CMEs) for trace analysis in aqueous and in 40% (v/v) ethanol-water media was investigated. Carbon paste electrodes modified with crown ethers were constructed by mixing the crown ethers into a graphite powder-paraffin oil matrix. The electrodes so formed were able to bind Cu(II) ions chemically and gave better voltammetric responses than the unmodified ones. The crown ethers studied and compared were 15-crown-5, benzo-15-crown-5 and dibenzo-18-crown-6. With a 3% benzo-15-crown-5 CME, Cu(II) could be quantified at sub-ppm levels by differential pulse voltammetry with a detection limit of 0.05 ppm. By differential pulse anodic stripping voltammetry Cu(II) could be quantified over the range I to 100 ppb. Interference from metal ions like Ni(II), Co(II), Mn(II), Fe(II), etc. have also been studied. The method was successfully applied to artificial as well as commercial samples of alcoholic beverages.
Copper(II) was selectively accumulated on a hanging mercury-drop electrode by using 2-mercaptobenzimidazole. Ensuing measurements were carried out by differential pulse adsorption stripping voltammetry. Factors affecting the accumulation, reduction, and stripping steps were investigated and a procedure was developed. The optimum conditions for the analysis of copper were pH 5.0, 5.33 x 10(-5) M 2-mercaptobenzimidazole and an accumulation potential of -0.10 V (vs. Av/AgCl). A linear range was obtained in the concentration range 0.2-100 ng/ml with a 90 s accumulation time and a scan rate of 16 mV/s. For ten successive determinations of 1.0, 20.0 and 70.0 ng/ml copper(II), relative standard deviations of 4.2, 3.5 and 2.8%, respectively, were obtained. The developed method was applied to the determination of copper in commercial salts and aluminium alloys.
Smoking is a present-day disease that affects a significant part of the world population and the search for analytical data regarding toxic elements in cigarettes is still an issue of analytical interest. This work describes an efficient, fast, and reliable analytical methodology for the determination of Cd, Pb and Cu in different constituent parts of cigarettes (filters, ashes, and tobacco) samples using Square Wave Anodic Stripping Voltammetry. The electrochemical system consisted of a cell with three electrodes: work – mercury film modified glassy carbon electrode, reference – Ag/AgCl(sat) and auxiliary – platinum, using as supporting electrolyte hydrochloric acid 10 mmol L⁻¹. The results obtained after the previous digestion of the samples in a microwave oven confirmed the efficiency of the procedure. The method was validated using 11 samples and the results showed recovery values between 80 and 111%. The accuracy was also evaluated by means of a matching reference sample of tomato leaves to prove the reliability of the method. The detection limits were 0.72, 0.89 and 1.43 μg L⁻¹ for Cd, Pb and Cu, respectively. Regarding the analytical results, the cadmium contents remained below the detection limits, while the average values found for lead were in the range 0.21, 2.84 and 4.86 μg/cigarette for the post-burning filter, ashes, and tobacco, respectively. The average values found of copper were in the range 0.49, 4.22 and 12.8 μg/cigarette for the post-burning filter, ashes, and tobacco, respectively.
Trace amounts of copper decrease significantly the oxidative stability of biodiesel while antioxidants, mostly tert-butylhydroquinone (TBHQ), are commonly introduced to the biofuel to guarantee induction period values within regulatory limits. Hence, a simple method to monitor the most used antioxidant and the most deleterious contaminant in biodiesel can give a fast response on its quality. In this context, this work presents a simple, efficient, low cost and sensitive method for the simultaneous and direct determination of copper and the antioxidant TBHQ in biodiesel. The biodiesel samples were diluted in 90% (v/v) ethanol and 10% (v/v) water containing 0.1 mol L ⁻¹ HCl (final concentration) as the supporting electrolyte generating a homogeneous mixture in which Cu(II) and TBHQ were directly detected using the square wave voltammetry (SWV) on a gold working electrode. The presence of biodiesel in the selected electrolyte facilitated the separation of analyte peaks facilitating the treatment of data and quantification. The linear responses for the simultaneous determination were in the range between 5 and 100 μg L ⁻¹ and 4.2–81.5 mg L ⁻¹ for copper and TBHQ (R > 0.997), respectively. High precision (RSD = 4.0% and 3.9%, n = 20) and limit of detection (LOD) values of 0.31 μg L ⁻¹ and 1.0 mg L ⁻¹ (0.030 μg g ⁻¹ and 0.102 mg g ⁻¹ in biodiesel) for Cu(II) and TBHQ, respectively, were obtained. Recovery values between 97% and 104% for both copper and TBHQ were obtained.
A platform for the determination of Zn(II), Cd(II), Pb(II) and Cu(II) has been proposed based on a novel diamond/graphite (D/G) nanoplatelets film electrode using differential pulse anodic stripping voltammetry method. The microstructure and the composition of the film were characterized by scanning electron microscope (SEM), atomic force microscope (AFM), Raman spectroscopy and transmission electron microscope (TEM). The D/G nanoplatelets structure with two-dimensional diamond nanoplatelet as the stem and highly conducting graphite layers as shells exhibits large specific surface and great electrical conductivity, significantly enhancing the electron transport in the electrochemical reaction. Under the optimum conditions, wide linear ranges and high sensitivity were achieved. In the typical detection process, two linear working ranges were obtained due to the incomplete anodic removal and the limits of detection (LODs) were estimated to be 1.72 μg L⁻¹, 0.47 μg L⁻¹, 4.86 μg L⁻¹ and 0.45 μg L⁻¹ for Zn(II), Cd(II), Pb(II) and Cu(II), respectively. The simultaneous detections also verify the superior analytical performance with linear ranges from 10 μg L⁻¹ to 250 μg L⁻¹ and low LODs. Herein, we present a novel diamond/graphite nanoplatelets electrode without any modification/functionalization for the sensitive detection of trace heavy metal ions.
Anodic stripping voltammetry (ASV) is an analysis technique that permits the selective and quantitative analysis of metal ion species in solution. It is most commonly applied in neutral to acidic electrolyte largely due to inherent metal ion solubility. Bismuth (Bi) is a common film used for ASV due to its good sensitivity, overall stability and insensitivity to O2. ASV, utilizing a Bi film, along with cadmium (Cd) and lead (Pb) as the plating mediators, has recently been adapted to determine zinc (Zn) concentrations in highly alkaline environments (30 % NaOH or 35 % M KOH). Successful analysis of Zn in alkaline relies on the ability of the hydroxide to form soluble metal anion species, such as Bi(OH)4− and Zn(OH)42−. Here, we look to extend this technique to detect and quantify copper (Cu) ions in these highly basic electrolytes. However, in general, the use of ASV to detect and quantify Cu ion concentrations is notoriously difficult as the Cu stripping peak potential overlays with that of Bi from the common Bi film electrode. Here, an ASV method for determining Cu concentration in alkaline solutions is developed utilizing Pb as a deposition mediator. As such, it was found that when analyzing Cu solutions in the presence of Pb, the stripping voltammetry curves present separate and defined Cu stripping peaks. Different analyzes were made to find the best stripping voltammetry performance conditions. As such, an accumulation time of 5 minutes, an accumulation potential of≤−1.45 V vs. Hg/HgO, and a concentration of 35 wt% KOH were determined to be the conditions that presented the best ASV results. Utilizing these conditions, calibration curves in the presence of 5.0 ppm Pb showed the best linear stripping signal correlation with an r-squared value of 0.991 and a limit of detection (LOD) of 0.67 ppm. These results give way to evaluating Cu concentrations using ASV in aqueous alkaline solutions.
The Group 11 is composed of copper (Cu), silver (Ag), and gold (Au). Silver and Au belong to the so-called noble metals. All these metals occur in variable oxidation stages, mainly +1, and +2, (Table II-11.1). Copper and Ag reveal chalcophilic tendencies whereas Au is siderophilic.
A new approach of double deposition and stripping steps was proposed in the course of anodic stripping lead ion determination in order to decrease the detection limit. Two bismuth film working electrodes differing in their surface area and mounted in one body were used for the measurements. In short, an ensemble of microelectrodes was centrally mounted in the electrode of a large surface area. The application of a new type of arrangement in combination with the additional deposition and stripping steps in one measurement cycle and in one electrochemical cell not only increased the sensitivity of determinations, but also facilitated the analysis. The obtained detection limit for the determination of lead ions following deposition time of 300 s at both working electrodes was 2.4 × 10⁻¹¹ mol L⁻¹. The proposed procedure was successfully applied for analysis of certified reference material that confirms the accuracy of the proposed methodology.
A procedure of Se(IV) determination by anodic stripping voltammetry using two deposition and stripping steps at gold electrodes was proposed. A well-defined stripping peak of selenium was obtained at potential 0.9 V. The optimization of parameters influencing the selenium peak current including both deposition and stripping steps was performed. A linear relationship was observed between the Se(IV) peak current and its concentration in the range from 5 × 10⁻⁹ to 1 × 10⁻⁷ mol L⁻¹. The limit of detection was found to be 8.5 × 10⁻¹⁰ mol L⁻¹. Repeatability of the method determined as RSD % for Se(IV) concentration of 5 × 10⁻⁸ mol L⁻¹ was 4.3 % (n = 7). The proposed procedure was used for Se(IV) determination in certified reference material and natural water samples and acceptable results and recoveries were obtained.
The reduced graphene oxide (RGO) and Chitosan (CS) hybrid matrix RGO-CS were coated onto the glassy carbon electrode (GCE) surface, then, poly-L-lysine films (PLL) were prepared by electropolymerization with cyclic voltammetry (CV) method to prepare RGO-CS/PLL modified glassy carbon electrode (RGO-CS/PLL/GCE) for the simultaneous electrochemical determination of heavy metal ions Cd(II), Pb(II) and Cu(II). Combining the advantageous features of RGO and CS, RGO and CS are used together because the positively charged CS can interact with the negatively changed RGO to prevent their aggregation. Furthermore, CS has many amino groups along its macromolecular chains and possessed strongly reactive with metal ions. Moreover, PLL modified electrodes have good stability, excellent permselectivity, more active sites and strong adherence to electrode surface, which enhanced electrocatalytic activity. The RGO-CS/PLL/GCE was characterized voltammetrically using redox couples (Fe(CN)63-/4-), complemented with electrochemical impedance spectroscopy (EIS). Differential pulse anodic stripping voltammetry (DPASV) has been used for the detection of Cd(II), Pb(II) and Cu(II). The detection limit of RGO-CS/PLL/GCE toward Cd(II), Pb(II) and Cu(II) is 0.01 μg L⁻¹, 0.02 μg L⁻¹ and 0.02 μg L⁻¹, respectively. The electrochemical parameters that exert influence on deposition and stripping of metal ions, such as supporting electrolytes, pH value, deposition potential, and deposition time, were carefully studied.
A simple and inexpensive anodic stripping voltammetric procedure for the determination of copper in dolomite, limestone and fly ash extracts is proposed. The method applies an antimony film electrode deposited in situ on a screenprinted graphite substrate. In the optimal conditions: 0.01 M acetate buffer (pH 4.5), 0.01 M KNO3, 0.25 mgL-1 Sb(III) and after 120 s of accumulation at a potential of -1.0 V, the procedure exhibits linear behavior from 4 to 200 μg L-1 Cu(II) with satisfying reproducibility (5%) and an LOD of 0.2 μg L-1.
The double deposition and stripping steps were proposed to minimize interference and increase the sensitivity in anodic stripping voltammetry of As(III). Two working electrodes of drastically different surface areas were used for the measurements. Arsenic was first deposited at the gold film electrode of a large surface area. When the deposition step at this electrode finished, the electrode was moved at a short distance to the second electrode consisting of four gold microelectrodes. The arsenic stripped from the first electrode was partially deposited at the microelectrodes and the analytical signal was obtained by its oxidation. Due to double deposition of arsenic the interference of Cu(II) was minimized and the detection limit of As(III) was lowered by one order of magnitude. The calibration graph was linear from 5×10−10 to 1×10−8 mol L−1 following deposition time of 300 s at the first and the second electrode.
A new way of decreasing the detection limit - double deposition and stripping steps was proposed to determine trace amounts of gold(III) by anodic stripping voltammetry. Two carbon composite electrodes that differed drastically in their surface areas were used for the measurements. The calibration graph was linear from 1×10−9 to 1×10−8 mol L−1 following deposition time of 300 s at the first and the second electrode. The detection limit was found to be 2.3×10−10 and 1.4×10−11 mol L−1 for deposition time 600 and 2400 s, respectively. It is the lowest detection limit obtained so far for gold(III) determination in stripping voltammetry.
An in-situ antimony film screen-printed carbon electrode (in-situ SbSPCE) was successfully used for the determination of Cu(II) simultaneously with Cd(II) and Pb(II) ions, by means of differential pulse anodic stripping voltammetry (DPASV), in a certified reference groundwater sample with a very high reproducibility and good trueness. This electrode is proposed as a valuable alternative to in-situ bismuth film electrodes, since no competition between the electrodeposited copper and antimony for surface sites was noticed. In-situ SbSPCE was microscopically characterized and experimental parameters such as deposition potential, accumulation time and pH were optimized. The best voltammetric response for the simultaneous determination of Cd(II), Pb(II) and Cu(II) ions was achieved when deposition potential was −1.2 V, accumulation time 120 s and pH 4.5. The detection and quantification limits at levels of μg L−1 suggest that the in-situ SbSPCE could be fully suitable for the determination of Cd(II), Pb(II) and Cu(II) ions in natural samples.
The Group 12 consists of zinc (Zn), cadmium (Cd), and mercury (Hg). These metals have quite a low abundance in the Earth’s crust. These metals form compounds in which their oxidation states are usually not higher than +2 and easily form metal-metal (+M-M+) bonds (Table II-12.1). The strength of the bond increases down the group, in the following order: Hg < Cd < Zn. The Zn 2 2+ and Cd 2 2+ ions are highly unstable, however, the +1 state of Hg is quite stable compared with the other two elements. The toxicity of Cd and Hg is well known, whereas Zn has enormous biological importance.
We report a very sensitive stripping voltammetric procedure for determination of ultra-trace quantity of U(VI) in water samples. A very low detection limit was achieved owing to the application of a new construction of the voltammetric electrode cell with two built-in working electrodes that differed significantly in their surface area. The procedure was based on the double adsorptive accumulation of the U(VI)-cupferron complex onto two lead film working electrodes. Under optimal conditions the detection limit for accumulation time of 120s for the big electrode and 120s for the small electrode was about 3.1×10(-11)molL(-1), whereas for accumulation time of 480s for the big electrode and 240s for the small electrode it was about 1.1×10(-11)molL(-1). The proposed method was successfully validated using certified reference material seawater NASS-5.
The double deposition and stripping steps were proposed to increase the sensitivity in anodic stripping voltammetry of lead and cadmium. Two in situ plated bismuth film electrodes at drastically different surface areas were used for the measurements. Cadmium and lead were at first deposited at the electrode with a large surface area. When the deposition step at the electrode was finished, the electrode was placed at a short distance opposite the small one. Then Cd(II) and Pb(II) stripped from the first electrode were deposited at the second electrode. Taking into account the small volume of space between the electrodes, the concentration of Pb(II) and Cd(II) between the electrodes was drastically higher than that in the bulk solution. The deposition step at the second electrode was performed from the solution with a higher concentration of the determined ions, and so the detection limit was lowered. Calibration was performed following deposition times of 300 and 120 s at the first and the second electrode, respectively. Under such conditions the detection limits of 1.8 × 10−10 and 4.5 × 10−11 mol L−1 for Pb(II) and Cd(II) were obtained, respectively.
The development and application of a functionalized carbon nanotubes paste electrode (CNPE) modified with crosslinked chitosan for determination of Cu(II) in industrial wastewater, natural water and human urine samples by linear scan anodic stripping voltammetry (LSASV) are described. Different electrodes were constructed using chitosan and chitosan crosslinked with glutaraldehyde (CTS-GA) and epichloro-hydrin (CTS-ECH). The best voltammetric response for Cu(II) was obtained with a paste composition of 65% (m/m) of functionalized carbon nanotubes, 15% (m/m) of CTS-ECH, and 20% (m/m) of mineral oil using a solution of 0.05 mol L −1 KNO 3 with pH adjusted to 2.25 with HNO 3 , an accumulation potential of −0.3 V vs. Ag/AgCl (3.0 mol L −1 KCl) for 300 s and a scan rate of 100 mV s −1 . Under these optimal experi-mental conditions, the voltammetric response was linearly dependent on the Cu(II) concentration in the range from 7.90 × 10 −8 to 1.60 × 10 −5 mol L −1 with a detection limit of 1.00 × 10 −8 mol L −1 . The samples analyses were evaluated using the proposed sensor and a good recovery of Cu(II) was obtained with results in the range from 98.0% to 104%. The analysis of industrial wastewater, natural water and human urine samples obtained using the proposed CNPE modified with CTS-ECH electrode and those obtained using a comparative method are in agreement at the 95% confidence level.
An antimony film electrode (SbFE) was prepared in situ on a glassy carbon support and in a new supporting electrolyte, a saturated solution of hydrogen potassium tartrate in which Sb(III) ions were complexed using tartrate. Its performance in anodic stripping voltammetric (ASV) determination of Cd(II), Pb(II), Zn(II), Tl(I), In(III) and Cu(II) traces was examined. It was found that 1.2 mg/L of Sb(III) yields the finest quality SbFE for analytical purposes. The procedure with in situ SbFE ensures well‐defined anodic stripping voltammetric curves of the investigated elements, low detection limits (0.5–3.8 µg/L), good reproducibility (1–5 %) and satisfactory sensitivity (32–184 nA/(µg/L)).
The suitability of ultrasound-assisted anodic stripping voltammetry (sono-ASV) for the detection of total copper content in beer using both mercury thin film and glassy carbon electrodes has been investigated. An immersion horn probe is introduced into a small thermostatted conventional three electrode cell (20 cm3) opposite the working electrode: an ex situ mercury plated Nafion®-coated mercury film electrode or a bare glassy carbon electrode. Minimal sample pre-treatment is required which consists of acidification of the beer with dilute nitric acid and out-gassing with argon. After the deposition of copper (as the metal or its amalgam) on the electrode in the presence of ultrasound, a square wave scan is employed to get the analytical signal. In the absence of ultrasound, electrode passivation by organic species and lower rates of mass transport prevent the observation of any measurable signals. In situ cavitational cleaning of the electrode by insonation maintains the electrode activity. Total copper content levels in the range of 100 to 300 µg Cu L–1 were determined by sono-ASV using both electrode substrates and showed excellent agreement with values provided by an independent method. This highlights the validity of the sono-ASV method as a useful electroanalytical technique in hostile media.
Natural zeolite modified carbon paste electrode (NZMCPE) was developed for the voltammetric determination of Cu (II). Copper (II) was selectively preconcentrated, at open circuit, on the NZMCPE. The measurements were carried out by using differential pulse cathodic stripping voltammetry. Linear response to copper (II) was found in the 5.0×10−8−5.0×10−6M (r: 0.9990) concentration range, with a detection limit estimated at 1.5×10−8M. The multiple determinations (n=6), following a preconcentration detection–regeneration cycle, shown a relative standard deviation of 2.22% at Cu (II) concentration of 2.0×10−6M. The developed method was also applied to the determination of copper in two model solutions and two real samples.
In this work, simultaneous determination of two groups of elements consisting of Pb(II)–Cd(II) and Cu(II)–Pb(II)–Cd(II) using adsorptive cathodic stripping voltammetry are described. The method is based on accumulation of these metal ions on mercury electrode using xylenol orange as a suitable complexing agent. The potential was scanned to the negative direction and the differential pulse stripping voltammograms were recorded. The instrumental and chemical factors were optimized using artificial neural network. The optimized conditions were obtained in pH of 5.5, xylenol orange concentration of 4.0μM, accumulation potential of −0.50V, accumulation time of 30s, scan rate of 10mV/s and pulse height of 70mV. The relationship between the peak current versus concentration was linear over the range of 5.0–150.0ngml−1 for cadmium and 5.0–150.0ngml−1 for lead. The limits of detection were 0.98 and 1.18ngml−1 for lead and cadmium ions, respectively. In simultaneous determination of Cu(II), Pb(II) and Cd(II) there are inter-metallic interactions, which result a non-linear relationship between the peak current and the ionic concentration for each of the element. Therefore, an artificial neural network was used as the multivariate calibration method. The ANN was constructed with three neurons as the output layer for the simultaneous determination of the three elements. The constructed model was able to predict the concentration of the elements in the ranges of 1.0–50.0, 5.0–200.0 and 10.0–200.0ngml−1, for Cu(II), Pb(II) and Cd(II), respectively.
In this paper, we report for the first time the characterization and separate electrochemical determinations of Cu2+ and Hg2+ directly on a microlithographically fabricated array of iridium ultramicroelectrodes (Ir-UMEA). Square-wave anodic stripping voltammetry was used to optimize experimental parameters such as supporting electrolyte, square-wave frequency, and deposition time and potential. Reproducible stripping peaks were obtained for solutions containing low parts per billion (ppb) concentrations of either metal. Excellent linearity was obtained for Cu2+ in the 20−100 ppb range and for Hg2+ in the 1−10 ppb range when the bare iridium substrate was used. Detection limits were calculated to be 1 ppb (0.1 M KNO3 and 0.1 M HClO4, deposition time 180 s) and 5 ppb (0.1 M H2SO4, deposition time 120 s) for Cu2+ (S/N = 3) and 85 ppt for Hg2+ (deposition time 600 s). The experimental detection limits were determined to be 5 ppb for Cu2+ (deposition time 180 s) and 100 ppt for Hg2+ (deposition time 600 s). Interference studies were performed, and it was determined that Pb, Zn, and Cd had little or no influence on the copper signal. Tap water and spring water samples were analyzed for copper, and good agreement was obtained with conventional methods. An unexplained effect of chloride ions on the iridium surface was noted. Further investigation by atomic force microscopy determined that changes on the surface occurred but could be eliminated when chloride leakage from the reference electrode was minimized. The solid state construction of the Ir-UMEA makes it a prime candidate for use in determining Cu(II) and Hg(II) in chemically harsh environments.
The complexing properties of ethylenediamine (en) were investigated as a means of performing the analysis of ligand-exchangeable and labile (i.e., directly reducible at pH 8) Cu in seawater at trace levels. Stripping polarographic or pseudopolarographic determinations show that the Cu-en complex behaves reversibly in seawater, exchanging two electrons at the mercury drop electrode (HMDE). The role of chloride ions in competitive reactions with en for copper during the stripping step was also studied. In seawater made 2 × 10-3 M in en, Cu(II) can be detected at the HMDE by differential pulse anodic stripping voltammetry (DPASV) at the 5 × 10-10 M level with a deposition time of 10 min. A new procedure for measuring pH 8 labile copper In seawater is obtained by coupling DPASV with a medium alteration method. Addition of en at the end of the electrolysis increases peak height by more than twice by doubling the current yield per mole of Cu and by removing interferences associated with the oxidation of Cu in Cl- media. This procedure facilitates the voltammetric study of Cu in seawater under natural conditions.
An adsorptive stripping voltammetric procedure for the determination of cobalt in a complex matrices at an in situ plated lead film electrode was described. The procedure exploits the enhancement effect of a cobalt peak observed in the system Co(II)–nioxime–piperazine-1,4-bis(2-ethanesulfonic acid)–cetyltrimethylammonium bromide. The calibration graph was linear from 5×10−10 to 2×10−8 mol L−1 and from 1×10−10 to 1×10−9 mol L−1 for the accumulation times 120 and 600 s, respectively. The detection limit (based on the 3 σ criterion) for Co(II) following accumulation time of 600 s was 1.1×10−11 mol L−1. The interference of high concentrations of foreign ions and surfactants was studied.
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].
The deposition and stripping processes of lead and copper and cadmium ions over the wide concentrations range of 1 × 10−5 to 5 × 10−9 M, have been studied at mercury film deposited on wax impregnated carbon paste electrode, using cyclic voltammetry, linear sweep anodic stripping voltammetry and differential pulse anodic stripping voltammetry. The carbon paste electrode modified with the mercury film was characterized for its physical and electrochemical properties. The parameters of deposition and stripping processes of the analytes have been investigated using standard solution of the metal ions at various concentrations and different supporting electrolytes and different pH. The linear sweep anodic stripping has been adopted for the determination of analytes at higher concentration whereas the analytes at lower concentrations were determined using DPASV. The DPASV behavior for the ions studied dependent on concentrations of the analyte as well as on the time used in the pre-concentration step. The method developed using standard solutions have been successfully applied for the determination of Cu(II), Pb(II) and Cd(II) in Fin Fish muscles and water samples.
Vermiculite clay mineral, a novel modifier, was exploited to prepare modified carbon paste electrodes (CPEs), showing attractive ability to efficiently preconcentrate trace copper(II) prior to its voltammetric determination. Under open-circuit conditions, copper(II) was preconcentrated onto the surface of a modified electrode via the ion-exchange capability of the modifier. After medium exchange to a pure electrolyte solution (0.1 M NaNO3 + Britton-Robinson buffer, pH 5), the accumulated copper(II) was reduced at −0.7 V vs. Ag/AgCl during an equilibration period of 20 s and then determined by its re-oxidation employing square-wave anodic stripping voltammetry. The parameters and conditions such as pH of the analyte solution and supporting electrolyte, preconcentration time, CPE composition, its activation and regeneration, stripping mode and others, were studied in detail. The detection limit (3σ) of the proposed procedure was found to be 5 × 10−9 mol l−1 of Cu(II) in the analyte solution, for a preconcentration time of 10 min. Applying suitable preconcentration times, a linear calibration graph from 1 × 10−8 mol l−1 to 8 × 10−5 mol l−1 (0.6 μg l−1−5.1 mg l−1) of Cu(II) was established. Multiple determinations (n = 10), following a preconcentration-measurement-regeneration cycle, gave a relative standard deviation of 4.9% at Cu(II) concentration of . The accuracy of the proposed method was checked by analysing a standard reference material (SRM 1643b).
The presence of trace metals in car fuels plays an important role in the engine maintenance. In addition, these metals contribute for the environmental contamination in big cities and their control is necessary. Square Wave Stripping Voltammetry (SWSV) is a very sensitive technique for elemental trace determination and was applied for ethanol fuel analysis. The first studies were done searching for the best conditions for copper determination in alcoholic medium, utilizing gold electrodes. During these studies, the possibility of the simultaneous determination of copper and lead in the same experiment was observed. Two procedures for the analysis of these metals were adopted: The direct quantification of metals in alcohol–water mixtures and a second way that involves the evaporation of the organic solvent and re-suspension of the ions with water+electrolyte. Good recovery values were obtained for synthetic samples spiked with known amounts of metals. The results obtained for the two methods were in good agreement. The detection limits for copper and lead in 75% ethanol–water ratio solution were calculated as 120 and 235 ng l−1, respectively, for 15-min deposition time.
A sensitive and selective procedure is presented for the voltammetric determination of copper. The procedure involves an adsorptive accumulation of copper pyrogallol red on a hanging mercury drop electrode, followed by a stripping voltammetric measurement of reduction current of adsorbed complex at −0.2 V (vs. Ag/AgCl). The optimum conditions for the analysis of copper include pH (3.0–4.5), 20 μM pyrogallol red and an accumulation potential of −0.1 V (vs. Ag/AgCl). The peak current is proportional to the concentration of copper over the range 0.4–60 ng ml−1 with a detection limit of 0.07 ng ml−1 with an accumulation time of 60 s. The method was applied to the determination of copper in some analytical grade salts and also in cow's liver tissue.
A rotating disc gold electrode is used for the determination of copper in μg l−1 and sub-μg l−1 concentrations without removal of oxygen by the method of subtractive anodic stripping voltammetry (SASV). The detection limit for a 90 s electrodeposition is 0.2 nM.The reduction and stripping of copper on gold under the SASV conditions are underpotential deposition/dissolution phenomena. A uniformly distributed submonolayer of copper, occupying 0.01–5% of the real surface of the electrode, is formed. Linearity in calibration plot is obtained up to 5% electrode coverage; in terms of the experimental parameters of the deposition step (rate of rotation and time of electrolysis), this condition for linearity is .The bulk and underpotential deposition of Cu2+ have been characterized in the supporting electrolyte used (10 mM HNO3 and 10 mM NaCl).The analysis of copper in drinking and in sea waters has been performed.
A gold electrode modified with a self-assembled monolayer (SAM) of 3-mercaptopropionic acid (MPA) was evaluated as a highly sensitive voltammetric sensor for copper ions. As demonstrated by cyclic voltammetric experiments, the SAM-based electrode showed an attractive ability to efficiently preconcentrate trace of copper(II) from solution, allowing a very simple and reproducible method for copper determination at levels down to ppq (parts per quadrillion). The influence of various experimental parameters on the sensor response was investigated (i.e. pH, supporting electrolyte, pre-concentration time). The MPA modified electrode presented a wide linear response range between 1.0×10−12 and 1.0×10−9 mol l−1 for copper(II), with a detection limit of 1.8×10−14 mol l−1 (1.1 pg l−1) using 10 min of pre-concentration. Moreover, this electrode also presented excellent repeatability, showing a relative standard deviation of 3.2% for a series of nine successive measurements of a 1.0×10−11 mol l−1 Cu2+ solution. This new sensor was successfully applied for the determination of copper in sugar cane spirits and mineral water samples.