Potentiometric stripping analysis for tin with a gold film electrode formed in situ on glassy carbon

A gold film electrode formed in situ on glassy carbon is used as the working electrode for the determination of tin over the range 0.1–10 μg ml^?1. Gold(III) added to the solution provides the film and serves as the oxidant for stripping. Two stripping curves corresponding to Sn(Au) → Sn(II) and Sn(II) → Sn(IV) were observed; either can be used for determinations of tin. The equations for the transition time (i.e., stripping signal) and stripping curve derived were verified experimentally.     

Determination of Trace Tin by Anodic Stripping Voltammetry at a Carbon Paste Electrode

A sensitive and selective procedure for the determination of trace tin at a carbon paste electrode was described. Each measurement cycle consisted of three steps: accumulation, reduction and stripping. The tin complex with bromopyrogallol red (BPR) was accumulated on the electrode surface in 0.10 mol/L acetate buffer (pH 4.5). After electrochemical reduction of Sn(II) had been carried out, the reoxidation wave of Sn(0) appeared at ?0.69 V (vs. SCE) on scanning the potential in the positive direction in 4.0 mol/L HCl. For a preconcentration time of 2 min, the detection limit was 0.06 μg/L (5×10^?10 mol/L ) and the linear range was from 0.1 to 50 μg/L. The proposed method was applied to the determination of tin in canned food and waste water samples with satisfactory results.     

Modified Glassy-Carbon Electrodes for the Flow-Injection Determination of Inorganic Tin Species by Stripping Voltammetry

The behavior of tin(II, IV) chloride species on an unmodified glassy-carbon electrode, and on or at film electrodes obtained by the electrooxidative modification of a glassy-carbon surface, in solutions of some polyphenols and other hydroxyl-containing aromatic compounds (salicylic acid and morin) was studied by cyclic voltammetry. The optimum conditions were found for the potentiostatic formation of films reproducible in thickness in the cyclic hydrodynamic mode. A comparison of the results of the studies demonstrated the effect of hydrophobic film nature on the redox processes observed in Sn(II, IV) and Pb(II) chloride solutions at different pHs. All the electrodes proposed preconcentrated tin(II) from flow solutions without applying a polarization voltage. The interfering effect of lead(II) was minimized by selecting an appropriate accumulation medium. The modified electrodes prepared by the electrooxidation of pyrogallol and morin were used for the flow-injection determination of trace amounts of Sn(II) in the presence of Sn(IV) and Pb(II) and for the determination of the total inorganic tin in model solutions by anodic stripping voltammetry.     

Simultaneous determination of tin and lead by anodic stripping voltammetry with addition of surfactant

The influence of various surfactants on the simultaneous determination of tin(IV)and lead(II) by differential-pulse stripping voltammetry at a hanging mercury drop electrode in an acidic medium is reported. With addition of Pluronic-F68 or Brij-78, the tin wave disappears, while the lead wave is not affected. With a deposition time of 1 min at ?0.8 V vs. Ag/AgCl, 10^?7 M concentrations of each ion can be determined if the Sn/Pb ratio is ? 3.     

Underpotential deposition of tin(II) on a gold disc electrode and determination of tin in a tin plate sample

This work describes a study of the underpotential deposition (UPD) of Sn²⁺ on a polycrystalline gold disc electrode using cyclic voltammetry (CV) and chronocoulometry (CC). Sn²⁺ ions showed well-defined peaks from UPD and UPD stripping (UPD-S) in 1 mol/L HCl solutions, while bulk deposition (BD) and BD stripping (BD-S) of the ions were also observed. The measured UPD shifts, E_UPD, between the UPD-S and the BD-S peaks were more than 200 mV. The UPD charge and the surface coverage of tin were measured by CC. A new method for determining Sn²⁺ was therefore developed, based on the excellent electrochemical properties of the Au/Sn UPD system. A plot of the UPD-DPASV (differential pulse anodic stripping voltammetry) signal versus the Sn(II) concentration was obtained for [Sn(II)] of 1.98×10^–7 to 3.64×10^–5 M. The method developed here has been applied to determine the tin in a tin plate sample.     

Determination of Gold, Silver, and Copper in Gold-Base Alloys by Potentiostatic Coulometry

The working conditions for the simultaneous coulometric determination of 0.5 to 3 mg of gold, silver, and copper with a relative standard deviation of at most 0.5% were found in the study of the voltammetric behavior of Au(III), Ag(I), and Cu(II) at a platinum electrode in a 2 M HCl + 0.1 M KCNS solution. Fivefold mass amounts of gold with respect to silver and copper did not interfere with their determination. The three elements can be triply determined in a single portion of a solution using the alternate cathodic and anodic polarization of the electrode ensuring the complete deposition and stripping of Au(0) and Ag(0) and the complete reduction and oxidation of Cu(II) Cu(I). The mechanism of current formation due to the chemical reaction of Au(I) disproportionation and its effect on the results of gold determination were studied using the current–time curves. Experimental conditions were proposed to eliminate this reaction. The procedure was used for determining the composition of ternary jewelry alloys containing different amounts of gold, silver, and copper without their preliminary separation.     

Simultaneous determination of tin and lead by a.c. anodic stripping voltammetry at a hanging mercury drop electrode sensitized by cetyltrimethylammoniu

The influence of cetyltrimethylammonium bromide (CTAB) on the simultaneous determination of tin(IV) and lead(II) by anodic stripping voltammetry at a hanging mercury drop electrode (HMDE) in a 0.1 M hydrochloric acid—0.1 M oxalic acid medium was studied using d.c. and a.c. stripping. In the presence of CTAB, tin and lead show voltammetric peaks separated by 100 mV, the sensitivity depending on the concentration of CTAB. The best conditions for the simultaneous determination of both elements (2 × 10^-3 M) were found. A method is proposed for the determination of tin in the presence of lead and three procedures are given for the determination of lead in the presence of tin.     

Metal film electrodes prepared with a reversibly deposited mediator in voltammetric analysis of metal ions

Electrochemical stripping analysis is recognized as a powerful technique for trace metals owing its remarkable sensitivity, relatively inexpensive instrumentation, ability for multielement determination and capable of determining elements accurately at trace and ultra-trace levels. The success of voltammetric sensing procedure depends mainly on the proper choice and preparation of the working electrode. The article reviews the development and application of metal film electrodes (bismuth, lead, and antimony film electrodes) prepared with a reversibly deposited mediator for stripping voltammetric determination of metal ions (Ni(II), Sn(IV), Hg(II), U(VI), Cd(II), Pb(II), and Cr(VI)). In this electrochemical, defect-mediated, thin-film growth method, the mediator is periodically deposited and the stripped from the surface, and this serves to significantly increase the density of islands of atoms of interest metal, what in consequence improves the electrochemical properties of these electrodes, because of the increase in the active surface area of electrode.     

Catalytic stripping analysis: sensitivity enhancement for reciprocal derivative constant-current stripping determination of palladium in the presence of tin(II) during stripping

The reciprocal derivative constant-current stripping signal of palladium at a mercury film electrode is increased, as in anodic stripping voltammetry (ASV), by a factor of ca. 80 if a certain amount of tin(II) is present in the stripping solution. This catalytic stripping phenomenon has been successfully used as a means of sensitivity enhancement in constant-current stripping determination of trace palladium. The limit of detection is 4 x 10(-10)M at S/N = 3, which is about two decades lower than that obtained without tin(II) present. Linear response was observed over the range 10(-10)-10(-7)M. This method has been applied to determine palladium in waste water and mineral samples. The experimental results support the postulated mechanism of signal enhancement, namely a chemical redeposition reaction occurring during the stripping, giving a cycle of stripping and deposition and thus increasing the stripping signal.     

Voltammetric stripping analysis of metal concentrates with polymers soluble in aqueous solutions

The conditions were worked out for the simultaneous stripping voltammetric determination of components of the ternary Pb(II)-Cu(II)-Cd(II) and binary Ag(I)-Cu(II) systems at a carbon-paste electrode in 2% aqueous solutions of the water soluble polymer polyethyleneimine (PEI) and its thiourea-containing derivative (TU-PEI). Water-soluble polymers are shown to reduce the mutual effects of the components of the binary and ternary system at the electrode surface. The different complex stability of Ag(I), Pb(II) or Cd(II) and Cu(II) with PEI and TU-PEI allows Ag(I), Pb(II) and Cd(II) to be determined in the presence of a large excess of Cu(II).     

1-(3-硝基苯基)-3-[4-(苯基偶氮)苯基]-三氮烯修饰碳糊电极测定痕量锡

制备了三氮烯修饰碳糊电极(m-NPPAPT/CPE),并研究了Sn(Ⅱ)在该电极上的吸附伏安行为,建立了一种测定痕量锡(Ⅱ)的新方法。采用二阶导数线性扫描溶出伏安法进行分析。结果表明:在1mL 0.5mol/L HCl溶液中,于-1200mV处搅拌富集一定时间,在-1200～-200mV范围内以150mV/s的扫描速度线性扫描,Sn(Ⅱ)吸附在修饰电极表面,于约-476mV(vs SCE)处产生一个灵敏的阳极溶出峰,峰电流比未修饰电极增大约11倍。其峰电流与Sn(Ⅱ)浓度在4.0×10-10～1.0×10-8 mol/L和1.0×10-8～4.0×10-6 mol/L范围内分两段呈良好线性关系,其线性回归方程分别为ip(μA)=1.646C(μmol/L)+2.9566和ip(μA)=52.804C(μmol/L)-0.6402,相关系数分别为0.9973和0.9967;检出限(S/N=3)为2.7×10-10 mol/L(富集时间120s)。本方法操作简便、灵敏度高,应用于罐头食品中锡含量的测定,结果满意。     

Voltammetry and controlled-potential coulometry with boron carbide electrodes

With the boron carbide electrode, E_{p$\text{p}\text{2}$} values were determined for the reduction of the following ions: Cd(II), Co(II), Cu(II), Fe(III), Ni(II), Pb(II), Ru(IV), Sb(V), and U(VI). The linear dependence of peak current on concentration is demonstrated for the U(VI) → U(IV) and Fe(III) → Fe(II) reductions at the boron carbide electrode. The suitability of the electrode for the controlled-potential coulometric ti trations of Fe(II) → Fe(III), Fe(III) → Fe(II), and U(VI) → U(IV) was studied; the results were inconclusive because of the small surface area that could be used conveniently and the possibility of oxygen leaks in the cell.     

Modification of a Pt surface by spontaneous Sn deposition for electrocatalytic applications

In the present communication we explored a simple dip-coating method for spontaneous (without applying an external current or additional reducing agents) modification of Pt surface by both tin oxy-species and tin metal based on hydrolysis of tin chloride complex and autocatalytic (electroless) deposition of tin for fabrication of the fuel cell catalysts with improved CO tolerance. It consisted of (i) Pt immersion into SnCl₂/HCl solution under open-circuit conditions; (ii) subsequent rinsing of the surface by pure water. The resulting Sn-modified Pt surfaces were characterized by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV). Two types of tin species, namely, tin oxide/hydroxide species and metallic tin were identified at Pt surface. Tin oxide/hydroxide species were assumed to be derived as a result of Sn(II) chloride complex hydrolysis, while tin metal particles were most likely deposited spontaneously on Pt surface due to disproportionation of Sn(II) to Sn(IV) and metallic tin, competing with dissolution of the Sn deposit in strongly acidic medium. Modifying tin species show a satisfactory stability in 0.5-M H₂SO₄ solution at potentials relevant to low-temperature fuel cell operating conditions (below 0.6 V vs. a standard hydrogen electrode, SHE).     

Coulometric Anodic Stripping Voltammetry of Lead at Copper Column Electrode

A flow coulometric electroanalytical system using a copper column electrode with a copper wire inserted into a Nafion tube was developed to determine Pb(II) content based on anodic stripping voltammetry. The electrolysis efficiency of 5 μM Pb(II) was evaluated to be 100.4±4.5 % (n=5) when the length of the copper wire and flow rate of the Pb(II) solution were 50 cm and 0.1 mL min⁻¹, respectively. The amount of electricity due to the re-oxidation of Pb electrodeposited at the copper column electrode was proportional to the concentration of Pb(II) in the range between 0.1 to 100 μM, and the limit of detection for Pb(II) was 0.8 μM for a deposition time of 15 min. Interference from the presence of Cd(II) could be avoided and the selective determination of Pb(II) was successfully achieved by adjustment of the electrodeposition potential.     

Voltammetric stripping analysis of metal concentrates with polymers soluble in aqueous solutions

The conditions were worked out for the simultaneous stripping voltammetric determination of components of the ternary Pb(II)-Cu(II)-Cd(II) and binary Ag(I)-Cu(II) systems at a carbon-paste electrode in 2% aqueous solutions of the water soluble polymer polyethyleneimine (PEI) and its thiourea-containing derivative (TU-PEI). Water-soluble polymers are shown to reduce the mutual effects of the components of the binary and ternary system at the electrode surface. The different complex stability of Ag(I), Pb(II) or Cd(II) and Cu(II) with PEI and TU-PEI allows Ag(I), Pb(II) and Cd(II) to be determined in the presence of a large excess of Cu(II). Received: 17 July 1997 / Revised: 1 December 1997 / Accepted: 3 December 1997     

Simultaneous Detection of Copper,Lead and Zinc on Tin Film/Gold Nanoparticles/Gold Microelectrode by Square Wave Stripping Voltammetry

In this work, three heavy metals (Cu(II), Pb(II) and Zn(II)) in wide potential window were simultaneously detected on tin film/gold nanoparticles/gold microelectrode (Sn/GNPs/gold microelectrode) by the method of square wave stripping voltammetry. The Sn/GNPs/gold microelectrode was fabricated by in situ plating of a Sn film on a gold nanoparticles (GNPs) modified gold microelectrode. The influence of hydrogen overflow on stripping of Zn(II) on the gold microelectrode was reduced by modification of GNPs, which made the stripping potential of target metals shift positively. The interference of sulfhydryl groups was reduced and the selectivity of the microelectrode was improved due to the addition of Sn in the detection solution. After accumulation at ?1.4 V for 300 s in acetate buffer solution (0.1 mol L^?1, pH 4.5), the Sn/GNPs/gold microelectrode revealed a good linear behavior in the examined concentration ranges from 5 to 500 µg L^?1 for Cu(II) and Pb(II), and from 10 to 500 µg L^?1 for Zn(II), with a limit of detection of 2 µg L^?1 for Cu(II), 3 µg L^?1 for Pb(II) and 5 µg L^?1 for Zn(II) (S/N=3). When compared with a Sb/GNPs/gold microelectrode and a Bi/GNPs/gold microelectrode, the Sn/GNPs/gold microelectrode showed the best stripping performance to Cu(II), Pb(II) and Zn(II). As a new type of environment‐friendly electrode, the Sn/GNPs/gold microelectrode has potential applications for detection of heavy metals.     

N → Sn coordination in the complexes of tin halides with pyridine: A comparison between Sn(II) and Sn(IV)

The experimentally well‐known complexation of tin(II) and tin(IV) halides with pyridine (py) leads to structures showing N → Sn coordination. In the present work, the complexes SnX_n·mpy (where X = F, Cl, Br, I; n = 2, 4; m = 1, 2) possessing this kind of coordination were studied using a computational quantum chemical approach. Various aspects in the theoretical picture of these complexes were examined to find similarities and differences in their N → Sn coordination. The aspects included, among others, the physical nature of intermolecular interactions, and their role in establishing the structure and energetic stabilization of the complexes. In this context, the effect of tin valency was inspected in great detail. As proven by several theoretical methods, a largely ionic character with a certain covalent component can be attributed to the studied N → Sn coordination, irrespective of tin valency. All complexes are destabilized by py‐py and three‐body interactions, but the Sn(II) complexes experience it to a greater extent. Marked differences are observed in the structural behavior of N → Sn and SnX_n during complex formation. This affects the energetics of complexation and, in consequence, the penta‐coordinated Sn(IV) center shows a higher propensity to expand its coordination number, compared with the tri‐coordinated Sn(II) center. The present study supplements the experimental characterization of SnX_n·mpy and, in general, it sheds light on the coordination of heteroaromatic nitrogen to tin. The survey of the Cambridge Structural Database revealed that such coordination occurred in a number of crystal structures.     

Differential pulse voltammetric determination of tin in the presence of noble metals

A voltammetric method for the determination of tin is proposed to minimise interferences from noble metals that are commonly encountered with other analytical techniques. Strong distortions of voltammetric peaks are observed in the presence of platinum. On the basis of a full investigation, the formation of an intermediate Sn(II)–Pt mixed chloro-complex at the electrode surface is identified as being responsible for the platinum interference, as it competes with the normal Sn(IV)→Sn(0)_Hg reduction. The use of a higher scan rate prevents the relatively low reaction kinetics and thus gets rid of this interference. No problems are encountered with other noble metals such as Pd, Ir, Re, Rh and Ru when using the modified method, although a baseline subtraction is necessary for the latter one. The proposed method is validated with real Pt–Sn catalysts.     

Preconcentration and electroanalysis of silver at pt electrode modified with poly(2-aminothiazole)

Conducting poly(2-aminothiazole) (PAT) films were electrodeposited on a platinum disc electrode surface by constant potential electrolysis of 2-aminothiazole (AT) for the stripping voltammetric determination of Ag(I). Ag(I) was preconcentrated on the polymer matrix by dipping the modified Pt electrode (PAT-Pt electrode) into Ag(I)(aq) solution. Effects of the film thickness, reduction potential, pH, preconcentration time, Ag(I) concentration and the interference of some other metal ions on the oxidation peak current of silver were studied. Cu(II) interference observed to be significant for the stripping voltammetric determination of Ag(I). The detection limit was calculated on the basis of signal to noise ratio of 3 as 2 × 10^?7 mol L^?1.     

Voltammetric study of the redox behaviour of the Hg(II)/Hg(I)/Hg system at a rotating metal-ring/glassy-carbon disc electrode

The reduction of Hg(II) at a glassy-carbon electrode in various electrolytes has been studied by rotating ring-disc voltammetry. Reduction proceeds directly to metallic mercury in a single 2-electron step. However, at the foot of the wave, and only during the first reduction sweep after pretreatment of the electrode surface, a small amount of Hg(I) species is detected at the ring. The appearance of an Hg(I) intermediate is most pronounced in sulphuric acid solution. The reduction of Hg(II) is found to proceed irreversibly and to be of first order. At sufficiently negative potentials the reduction is convective-diffusion controlled. Stripping voltammetric experiments indicate that the dissolution of mercury gives Hg(II) in complexing electrolytes. In non-complexing electrolytes the initially formed Hg(II) reacts with mercury atoms on the electrode surface to give Hg(I). During electrodissolution, two stripping peaks may be observed as a result of underpotential adsorption of mercury on glassy carbon. The difference in peak potential between the adsorption (mono) layer peak and the bulk mercury peak has been related to the difference in work functions of the deposit (mercury) and substrate (carbon). A rotating glassy-carbon electrode has been used for the anodic stripping determination of mercury. When an appropriate amount of a cation such as cadmium(II) or copper(II) is added to the test solution, mercury down to 2 x 10(-9)M (0.4 ng ml ) can be determined in acidified thiocyanate electrolyte with a relative standard deviation of about 22%.