H-point standard addition method in the analysis by differential pulse anodic stripping voltammetry Simultaneous determination of lead and tin

The applicability of H-point standard addition method (HPSAM) to the resolving of overlapping differential pulse anodic stripping voltammetric peaks corresponding to the oxidation of lead and tin is verified. The results show that the H-point standard addition method is suitable for the simultaneous determination of lead and tin in aqueous media. The results of applying the H-point standard addition method showed that Sn²⁺ and Pb²⁺ could be determined simultaneously with the concentration ratios of Sn²⁺ to Pb²⁺ varying from 1:5 to 10:1 in the mixed sample. The proposed method has been successfully applied to the simultaneous determination of lead in the presence of tin in some synthetic samples. Moreover, the applicability of the method was demonstrated by the recovery of lead in a canned soft drink sample.     

Simultaneous determination of copper, zinc and lead by adsorptive stripping voltammetry in the presence of Morin

A sensitive and selective method for the simultaneous determination of copper, zinc and lead is presented. The method is based on the adsorptive accumulation of 2′,3,4′,5,7-pentahydroxyflavone (Morin) complexes of these elements onto a hanging mercury drop electrode, followed by reduction of adsorbed species by voltammetric scan using differential pulse modulation. Optimal analytical conditions were found to be Morin concentration of 2.0 μM, pH of 4.0, and an adsorption potential at −500 mV versus Ag/AgCl. With an accumulation time of 60 s, the peak currents are proportional to the concentration of copper, lead and zinc over the 1 to 60, 0.3-80 and 1-70 ng ml⁻¹ range with detection limits of 0.06, 0.08 and 0.06 ng ml⁻¹, respectively. The procedure was applied to the simultaneous determination of copper, lead and zinc in some real and synthetic artificial real samples with satisfactory results.     

Simultaneous determination of mercury and arsenic by anodic stripping voltammetry

An electrochemical method for the simultaneous determinations of Hg^II concentration and total As^III and As^V concentration has been developed. The method does not require the additional preliminary step of the chemical reduction of As^V to As^III, or oxidation of As^III to As^V before stripping analysis takes place. Also, the method for the simultaneous determination of Hg^II concentration and As^III concentration is described. Measurements were performed in 0.1 M HCl using a gold-plated graphite electrode as sensor. Detection limits for both methods are below 0.4 ppb. Relative standard deviation did not exceed 15%. The possible interference by other trace metals was investigated. Analyses of natural water and industrial solutions were made using proposed methods and AAS. The t-test demonstrates that there was no significant difference between the results obtained with these methods. Proposed methods decrease the time of analysis because concentrations of the Hg^II and arsenic ions were measured simultaneously. Also, the removal of the additional step of chemical reduction of As^V to As^III or oxidation of As^III to As^V decreases analysis time, and also reduces the chance of contamination due to the use of additional reagents.     

Copper determination in ethanol fuel by differential pulse anodic stripping voltammetry at a solid paraffin-based carbon paste electrode modified with 2-aminothiazole organofunctionalized silica

Solid paraffin-based carbon paste electrodes modified with 2-aminothiazole organofunctionalized silica have been applied to the anodic stripping determination of copper ions in ethanol fuel samples without any sample treatment. The proposed method comprised four steps: (1) copper ions preconcentration at open circuit potential directly in the ethanol fuel sample; (2) exchange of the solution and immediate cathodic reduction of the absorbate at controlled potential; (3) differential pulse anodic stripping voltammetry; (4) electrochemical surface regeneration by applying a positive potential in acid media. Factors affecting the preconcentration, reduction and stripping steps were investigated and the optimum conditions were employed to develop the analytical procedure. Using a preconcentration time of 20 min and reduction time of 120 s at −0.3 V versus Ag/AgCl_sat a linear range from 7.5 × 10⁻⁸ to 2.5 × 10⁻⁶ mol L⁻¹ with detection limit of 3.1 × 10⁻⁸ mol L⁻¹ was obtained. Interference studies have shown a decrease in the interference effect according to the sequence: Ni > Zn > Cd > Pb > Fe. However, the interference effects of these ions have not forbidden the application of the proposed method. Recovery values between 98.8 and 102.3% were obtained for synthetic samples spiked with known amounts of Cu²⁺ and interfering metallic ions. The developed electrode was successfully applied to the determination of Cu²⁺ in commercial ethanol fuel samples. The results were compared to those obtained by flame atomic absorption spectroscopy by using the F-test and t-test. Neither F-value nor t-value have exceeded the critical values at 95% confidence level, confirming that there are no significant differences between the results obtained by both methods.     

Significance of data treatment and experimental setup on the determination of copper complexing parameters by anodic stripping voltammetry

Different procedures of voltammetric peak intensities determination, as well as various experimental setups were systematically tested on simulated and real experimental data in order to identify critical points in the determination of copper complexation parameters (ligand concentration and conditional stability constant) by anodic stripping voltammetry (ASV). Varieties of titration data sets (Cu_measuredvs. Cu_total) were fitted by models encompassing discrete sites distribution of one-class and two-class of binding ligands (by PROSECE software). Examination of different procedures for peak intensities determination applied on voltammograms with known preset values revealed that tangent fit (TF) routine should be avoided, as for both simulated and experimental titration data it produced an additional class of strong ligand (actually not present). Peak intensities determination by fitting of the whole voltammogram was found to be the most appropriate, as it provided most reliable complexation parameters.Tests performed on real seawater samples under different experimental conditions revealed that in addition to importance of proper peak intensities determination, an accumulation time (control of the sensitivity) and an equilibration time needed for complete complexation of added copper during titration (control of complexation kinetics) are the keypoints to obtain reliable results free of artefacts.The consequence of overestimation and underestimation of complexing parameters is supported and illustrated by the example of free copper concentrations (the most bioavailable/toxic specie) calculated for all studied cases. Errors up to 80% of underestimation of free copper concentration and almost two orders of magnitude overestimation of conditional stability constant were registered for the simulated case with two ligands.     

Determination of lead and cadmium using a polycyclodextrin-modified carbon paste electrode with anodic stripping voltammetry

This work reports the use of and -cyclodextrin-modified carbon paste electrodes (CPE_-CD and CPE_-CD) to determine simultaneously Pb(II) and Cd(II) by means of the electrochemical technique known as anodic stripping voltammetry (ASV). Both modified electrodes displayed good resolution of the oxidation peaks of the said metals. Statistic analysis of the results strongly suggests that the CPE_-CD exhibited a better analytical response that the CPE_-CD, while the detection limits obtained for Pb(II) were 6.3×10^–7 M for the CPE_-CD and 7.14×10^–7 M for the CPE_-CD, whereas for Cd(II) they were 2.51×10^–6 M for the CPE_-CD and 2.03×10^–6 M for the CPE_-CD.     

Individual and simultaneous determination of lead, cadmium, and zinc by anodic stripping voltammetry at a bismuth bulk electrode

A bismuth bulk electrode (BiBE) has been investigated as an alternative electrode for the anodic stripping voltammetric (ASV) analysis of Pb(II), Cd(II), and Zn(II). The BiBE, which is fabricated in-house, shows results comparable to those of similar analyses at other Bi-based electrodes. Metal accumulation is achieved by holding the electrode potential at −1.4 V (vs. Ag/AgCl) for 180 s followed by a square wave voltammetric stripping scan from −1.4 to −0.35 V. Calibration plots are obtained for all three metals, individually and simultaneously, in the10-100 μg L⁻¹ range, with a detection limit of 93, 54, and 396 ng L⁻¹ for Pb(II), Cd(II), Zn(II), respectively. A slight reduction in slope is observed for Cd(II) and Pb(II) when the three metals are calibrated simultaneously vs. individually. Comparing the sensitivities of the metals when calibrated individually vs. in a mixture reveals that Zn(II) is not affected by stripping in a mixture. However, Pb(II) and Cd(II) have decreasing sensitivities in a mixture. The optimized method has been successfully used to test contaminated river water by standard addition. The results demonstrate the ability of the BiBE as an alternative electrode material in heavy metal analysis.     

Determination of cadmium, lead, copper and zinc in the acetic acid extract of glazed ceramic surfaces by anodic stripping voltammetric method

An anodic stripping voltammetric method has been developed for determination of cadmium, lead, copper and zinc in acetic acid extract of glazed ceramic surfaces. An aliquot of 4% (v/v) acetic acid solution was kept in a ceramic ware for 24 h in the dark, then 10 mL of the extracted solution was placed in a voltammetric cell. The solution was purged with oxygen free nitrogen gas for 3 min before deposition of the metals was carried out by applying a constant potential of −1.20 V versus Ag/AgCl to the hanging mercury drop electrode (HMDE) for 45 s. A square wave waveform was scanned from −1.20 to 0.15 V and a voltammogram was recorded. A standard addition procedure was used for quantification. Detection limits of 0.25, 0.07, 2.7 and 0.5 μg L⁻¹ for cadmium, lead copper and zinc, respectively, were obtained. Relative standard deviations for 11 replicate determinations of 100 μg L⁻¹ each of all the metals were in the range of 2.8-3.6%. Percentage recoveries obtained by spiking 50 μg L⁻¹ of each metal to the sample solution were in the range of 105-113%. The method was successfully applied to ceramic wares producing in Lampang province of Thailand. It was found that the contents of cadmium, lead, copper and zinc released from the samples were in the range of <0.01-0.16, 0.02-0.45, <0.14 and 0.28-10.36 μg dm⁻², respectively, which are lower than the regulated values of the Thai industrial standard. The proposed method is simpler, more convenient and more sensitive than the standard method based on FAAS.     

Simultaneous determination of copper and lead in seawater using optimised thin-mercury film electrodes in situ plated in thiocyanate media

In the present work the anodic stripping voltammetric (ASV) methodology using a thin mercury film electrode in situ plated in thiocyanate media was re-assessed in order to allow the simultaneous determination of copper and lead in seawater. Under previously suggested conditions [6], i.e. using a concentration of thiocyanate of 5 mM, the ASV peaks of copper and lead overlapped due to the formation of a stable copper(I)-thiocyanate species, limiting the analytical determinations. Therefore, the best value for the thiocyanate concentration was re-evaluated: for 0.05 mM a trade-off between good resolution of the copper and lead peaks and high reproducibility of the mercury film formation/removing processes was achieved. In this media, the ASV peaks for Pb and Cu occurred, separated by 140 mV. Also, the in situ thin mercury film electrode was produced and removed with good repeatability, which was confirmed by the relative standard deviation values for the ASV determinations: 0.5% for Pb and 2.0% for Cu (10 replicate determinations in a solution with metal concentrations 1.5×10⁻⁸ M for lead and 2.2×10⁻⁸ M for copper). The optimised methodology was successfully applied to the determination of copper in the presence of lead, in certified seawater (NASS-5).     

Determination of sub-micromolar amounts of sulfide by standard free anodic stripping voltammetry and anodic stripping voltammetric titration

A novel electrochemical methods namely standard free anodic stripping voltammetry and anodic stripping voltammetric titration are proposed for determination of dissolved sulfide concentration. 2Ag⁺ + S²⁻ → Ag₂S reaction is used to provide the information. The anodic stripping voltammetric response of unreacted silver-ions at the glassy carbon electrode is used as analytical signal. Results reliability and accuracy are confirmed by analysis of model solutions, spiked natural and tap waters and recovery study, with a recovery of 100 ± 5% (n = 7) obtained. The approaches show the detection limit (3σ_blank) of 2-5 × 10⁻¹⁰ mol L⁻¹ and the relative standard deviation of 2-5% for repeated measurements.     

Determination of anionic surfactants by bis(ethylenediamine)copper(II) extraction and anodic stripping voltammetry

A stripping voltammetric finish for the measurement of total anionic surfactant has been developed. A limit of detection of 5.0 μg 1^?1 anionic surfactant was observed with a linear calibration from 5.0 to 500 μg 1^?1 in the original sample.     

Direct determination of cadmium and lead in pharmaceutical ingredients using anodic stripping voltammetry in aqueous and DMSO/water solutions

A new electrochemical method has been developed to detect and quantify the elemental impurities, cadmium(II) (Cd²⁺) and lead(II) (Pb²⁺), either simultaneously or individually in pharmaceutical matrices. The electro-analytical approach, involving the use of anodic stripping voltammetry (ASV) on an unmodified glassy carbon electrode, was performed in both aqueous and in a 95/5 dimethyl sulfoxide (DMSO)/water solutions, without acid digestion or dry ashing to remove organic matrices. Limits of detection (LODs) in the μg L⁻¹ [or parts per billion (ppb), mass/volume] range were obtained for both heavy metals - in the presence and absence of representative pharmaceutical components. To the best of our knowledge, the work demonstrates the first analysis of heavy metals in DMSO/water solutions through ASV. The strong reproducibility and stability of the sensing platform, as well as obviation of sample pretreatment show the promise of utilizing ASV as a sensitive, robust, and inexpensive alternative to inductively-coupled-plasma (ICP)-based approaches for the analysis of elemental impurities in, e.g., pharmaceutical-related matrices.     

Antimony-film electrode for the determination of trace metals by sequential-injection analysis/anodic stripping voltammetry

The possibility of applying antimony-film modified glassy carbon electrode in sequential-injection analysis (SIA) was investigated with the objective of determining Pb(II) and Cd(II) by anodic stripping voltammetry (ASV). The conditions of antimony-film deposition concerning composition of the plating/carrier solutions, concentrations of Sb(III) and hydrochloric acid, effects of different supporting electrolyte salts, and plating potential were optimized. It was found that the antimony-film deposition on glassy carbon substrate in a sample solution consisting of 750 μg L⁻¹ Sb(III), 0.5 mol L⁻¹ HCl at −1.5 V (vs. Ag/AgCl/3 mol L⁻¹ KCl) yielded a modified electrode suitable for the determination of Pb(II) and Cd(II) at the μg L⁻¹ level. The reproducibility of the analytical signals was characterized by a relative standard deviation lower than 2.8%, and the calculated values of detection limits were 1.2 μg L⁻¹ for Pb(II) and 1.4 μg L⁻¹ for Cd(II). The presence of KSCN in the sample solution offers the possibility of detecting ions with more negative oxidation potentials like Zn(II), Mn(II) or Cr(III). The developed SIA-ASV procedure was compared with the commonly used batch method, and its applicability was tested on a spiked tap water sample.     

Quantitative determination of zinc in milkvetch by anodic stripping voltammetry with bismuth film electrodes

Bismuth film electrode (BiFE) was shown to be an attractive alternative to common mercury film electrode (MFE) for anodic stripping voltammetric measurements. In this study, bismuth film, that was in situ deposited onto glassy carbon electrode, was used to detect zinc content of milkvetch, used in traditional Chinese medicine. Variables affecting the response have been evaluated and optimized. Experimental results showed a high response, with a good linearity (between 0.5 × 10⁻⁶ mol L⁻¹ and 3 × 10⁻⁶ mol L⁻¹) a good precision (R.S.D. = 3.58%) and a low detection limit (9.6 × 10⁻⁹ mol L⁻¹ with a 120 s anodic). The anodic stripping performance makes the bismuth film electrode very desirable for measurements of trace nutritive element zinc in milkvetch and should impart possible restrictions on the use of mercury electrode.     

Functioning of antimony film electrode in acid media under cyclic and anodic stripping voltammetry conditions

New insights into the functioning, i.e. electrochemical behaviour and analytical performance, of in situ prepared antimony film electrodes (SbFEs) under square-wave anodic stripping (SW-ASV) and cyclic (CV) voltammetry conditions are presented by studying several key operational parameters using Pb(II), Cd(II) and Zn(II) as model analyte ions. Five different carbon- and metal-based substrate transducer electrodes revealed a clear advantage of the former ones while the concentration of the precursor Sb(III) ion exhibited a distinct influence on the ASV functioning of the SbFE. Among six acids examined as potential supporting electrolytes the HNO₃ was demonstrated to yield nearly identical results in conducting ASV experiments with SbFE as so far almost exclusively used HCl. This is extremely important as HNO₃ is commonly employed acidifying agent in trace metal analysis, especially in elemental mass spectrometry measurements. By carrying out a systematic CV and ASV investigation using a medium exchange protocol, we confirmed the formation of poorly soluble oxidized Sb species at the substrate electrode surface at the end of each stripping step, i.e. at the potentials beyond the anodic dissolution of the antimony film. Hence, the significance of the cleaning and initializing the surface of a substrate electrode after accomplishing a stripping step was thoroughly studied in order to find conditions for a complete removal of the adhered Sb-oxides and thus to assure a memory-free functioning of the in situ prepared SbFE. Finally, the practical analytical application of the proposed ASV method was successfully tested and evaluated by measuring the three metal analytes in ground (tap) and surface (river) water samples acidified with HNO₃. Our results approved the appropriateness of the SbFE and the proposed method for measuring low μg L⁻¹ levels of some toxic metals, particularly taking into account the possibility of on-field testing and the use of low cost instrumentation.     

Determination of trace metoclopramide by anodic stripping voltammetry with nafion modified glassy carbon electrode

A novel method is described for determination of metoclopramide (MCP) by second-derivative adsorptive anodic stripping voltammetry with a nafion-modified electrode. The stripping peak current is proportional to the concentration of MCP over the range 1.2×10⁻⁹–4.6×10⁻⁷ M. The detection limit is 8.0×10⁻¹¹ M with 4-min accumulation. The method has been successfully applied to the determination of MCP in human serum.     

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

Summary 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.

---

Simultanbestimmung von Blei, Cadmium und Zink in Aerosolen durch anodische Stripping-Voltammetrie

Zusammenfassung Die optimalen Bedingungen für die Bestimmung von Pb, Cd und Zn unter Verwendung von Ammoniumtartratpuffer pH 4,5 wurden ausgearbeitet. Störungen durch andere Metalle traten bei den untersuchten Aerosolen nicht auf. Die Standardabweichungen lagen bei ±10%. Infolge niedriger Blindwerte und hoher Empfindlichkeit konnten Bestimmungen im sub-ppb-Bereich mit Elektrolysenzeiten von 3–10 min durchgeführt werden. Ein Überblick über die Konzentration der genannten Metalle in der Luft von Bombay wird gegeben.

     

A detailed investigation for determination of tannic acid by anodic stripping voltammetry using porous electrochemical sensor

The electrochemical responses of tannic acid have been obtained at porous pseudo-carbon paste electrode (PPCPE), polypyrrole modified carbon paste electrode (PCPE), SBA-15 modified CPE (SBA-MCPE) and carbon paste electrode (CPE) under same conditions, respectively. The results show that the sensitivity of PPCPE is the highest among all the checked electrodes. The detection limit at PPCPE is 0.01 μM, which is about 10 times lower than that at CPE and is about 5 times lower than that at PCPE or SBA-MCPE. The developed electrode PPCPE possesses a few obvious advantages and no binding reagents are needed. The surface area of PPCPE is 59.26 m² g⁻¹ with pores ranging from 2 to 5 μm in diameter. The PPCPE is easy to preserve and has good reusability, which affords a nice electrochemical platform for detecting tannic acid.     

茜素红S/多壁碳纳米管修饰碳糊电极阳极溶出伏安法测定痕量铜

制备了茜素红S/多壁碳纳米管修饰碳糊电极,提出了一种灵敏的溶出伏安法测定痕量铜的新方法.在极谱分析仪上采用二阶导数线性扫描伏安法进行分析,在0.1 moL/L的HAc-NaAc缓冲溶液(pH 4.1)中,Cu与修饰电极表面的茜素红S(ARS)形成Cu(Ⅱ)-ARS络合物而富集于电极表面,于-400 mV处还原后,再进行阳极化扫描,于64 mV处获得一灵敏的铜的阳极溶出峰,峰电流与Cu(Ⅱ)浓度在2×10-11 mol/L～6×10-7 mol/L范围内呈良好的线性关系,检出限(S/N=3) 为8.0×10-12 mol/L(富集时间240 s).方法应用于人发中铜含量的测定,回收率为98%～102%.     

Metal analysis in real matrices. Simultaneous voltammetric determination of copper and antimony in alloys

This work addresses the simultaneous determination of copper(II) and antimony(III) in real matrices by differential pulse (DPASV) and fundamental harmonic alternating current anodic stripping voltammetry (ACASV). The voltammetric measurements were carried out using as supporting electrolyte the same acidic mixture (nitric, hydrochloric and perchloric acids) used in the dissolution of the real matrices with proper dilution. The procedure of the sample preparation is thus reduced to one step hence avoiding errors from long and complex sample handlings prior to the instrumental measurement. The results were verified by the analysis of the standard reference materials NBS-SRM 631 Spectrographic Zinc Spelter D-2 and BCS 207/2 Gunmetal. The precision, expressed as relative standard deviation, and the accuracy, expressed as relative error, were, in all cases, less than 5%; the detection limit, for each element and in the experimental conditions employed, was around 10⁻⁷ M. The standard addition technique improved the resolution of the voltammetric method, even in the case of very high metal concentration ratios.