Subtractive differential pulse anodic stripping voltammetry at a stationary mercury-coated glassy carbon electrode

The application of subtractive mode differential pulse anodic stripping voltammetry (SDPASV) at a stationary mercury-coated glassy carbon electrode for the analysis of labile Zn(II), Cd(II), Pb(II) and Cu(II) is described. It is shown that the method has an improved sensitivity to Cu(II) owing to elimination of high background currents normally encountered in normal mode DPASV at the TFME. The sensitivity limits of the present method to Cd(II) and Cu(II) is estimated to be 0.025 and 0.067 ppb respectively, when a 2 min deposition time is used. It is suggested that the high sensitivity of the method coupled to the relative simplicity of the stationary electrodes could make the method useful in environmental and natural water studies.     

Determination of thallium in lead salts by differential pulse anodic-stripping voltammetry

The determination of trace levels of thallium in lead and lead salts by differential pulse anodic-stripping voltammetry has been made possible by using a surfactant as an electrochemical masking agent in addition to a complexing agent. In 0.2M EDTA at pH 4.5 as supporting electrolyte without surfactant, lead at concentrations below 0.5mM does not give a peak. When the electrolyte also contains tetrabutylammonium chloride (TBAC) at 0.01 M concentration, lead can be tolerated at concentrations up to 0.05M, while the height of the thallium peak is unaffected. It is thus possible to determine 5nM T1(I) in the presence of 0.05M Pb(II), i.e., Tl at the 1 x 10(-5)% level in lead. The precision of the determination (1-4%) and the recovery are satisfactory. Neither an 800-fold excess ratio of Cu(II) to Tl(I) nor a 10(7)-fold ratio of Bi(III) interferes in the determination. Thallium has been determined in a range of lead salts of various degrees of purity.     

Determination of arsenic in polluted waters by differential pulse anodic-stripping voltammetry

Experimental parameters affecting the analytical response of arsenic in differential pulse anodic-stripping voltammetry (DPASV) have been examined. DPASV offers higher sensitivity than linear-scan anodic-stripping voltammetry for similar analysis times. Both techniques have been applied to the NBS Standard Reference Water (SRM 1643) and some polluted water samples. The results on polluted waters compared favourably with those obtained by graphite-furnace atomic-absorption spectroscopy.     

Evaluation of differential pulse voltammetry at carbon electrodes

The background and analytical responses of differential pulse voltammetry at carbon electrodes have been evaluated. Transient currents associated with small potential steps have been examined and are attributed mainly to redox reactions of various groups on the electrode surface. Instrumental parameters have been thoroughly investigated and optimized for improving the signal-to-background response. Glassy-carbon and carbon-paste disk electrodes have been compared, and the latter found to yield better response owing to the lower background current. Dopamine, epinephrine, chlorpromazine, ascorbic acid, homovanillic acid and ferrocyanide were used as test systems.     

Preconcentration and differential pulse voltammetry of butylated hydroxyanisole at a carbon paste electrode

Butylated hydroxyanisole (BHA) and other tocopherols are shown to accumulate very strongly onto carbon paste, with the surface species retaining their characteristic electroactivity. This accumulation serves as a preconcentration step which improves the voltammetric measurement with respect to the sensitivity and selectivity. After 5-min preconcentration, a detection limit near 2 × 10^?8 M BHA is obtained. Enhanced selectivity is achieved if the electrode is transferred into an electrolytic blank solution between the preconcentration and measurement steps. The accumulated analyte can then be quantified in the presence of a 10³-fold amount of a solution species with similar redox potential. The differential pulse stripping response is evaluated with respect to concentration dependence, reproducibility, preconcentration period, detection limit, and other variables. The preconcentration/medium exchange approach is exploited for selective detection of BHA in a flow injection system. Applicability to various real samples is illustrated.     

Determination of thallium in bismuth by differential pulse anodic-stripping voltammetry without preliminary separation

The determination of trace levels of thallium in bismuth and bismuth salts by differential pulse anodic-stripping voltammetry has been made possible by using a surfactant as an electrochemical masking agent, in addition to a complexing agent. In 0.2M EDTA at pH 4.5 as supporting electrolyte in the absence of surfactant, bismuth at concentrations below 10(-4)M does not interfere. When the electrolyte also contains tetrabutylammonium ions at 0.01 M concentration, bismuth can be tolerated at concentrations up 0.05M, and the height of the thallium peak is unaffected. It is thus possible to determine 1 nM Tl(I) in the presence of 0.05M Bi(III), i.e., Tl at the 1 x 10(-6)% level in bismuth. The precision of the determination and the recovery are satisfactory. Neither an 800-fold ratio of Cu(II) nor a 10(7)-fold ratio of Pb(II) to Tl(I) interferes in the determination. Other cations such as Zn(2+), Cd(2+), In(3+), Hg(2+), Fe(3+), Sb(3+) and Sn(4+) in 10(4)-fold molar ratio to Tl(I) have no effect on the determination. Thallium has been determined in bismuth metal and in bismuth nitrate of various degrees of purity.     

Determination of phenol by differential pulse voltammetry with a sepiolite-modified carbon paste electrode

Summary The determinations of phenol is studied by means of a carbon paste electrode modified with 10% sepiolite using DPV. A 10 min preconcentration step was performed at pH 1.5 under open circuit conditions. Measurements were made in another cell by DPV with E=100 mV (sweep rate = 40 mV/s) in 0.02 mol/l KNO₃ medium at pH 2. Detection limits (3 ) of 30 ng/ml were achieved for determinations in orange, lemon and cola drinks.

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Phenolbestimmung durch Differentialpuls-Voltammetrie mit einer Sepiolit-modifizierten Kohlepaste-Elektrode

     

Determination of thallium at subtrace level in rocks and minerals by coupling differential pulse anodic-stripping voltammetry with suitable enrichment methods

Ten international reference samples have been analysed for thallium content by differential pulse anodic-stripping voltammetry. Two separation techniques, solvent extraction and ion-exchange, were employed to preconcentrate the thallium: the results were critically compared to establish which was the better separation technique. The values found were quite satisfactory and confirmed the wide scope for application (not yet fully investigated) of voltammetry in geochemical studies.     

Investigation by automated differential pulse anodic-stripping voltammetry of the problem of storage of dilute solutions

The storage of dilute solutions of metal ions before their laboratory analysis presents a difficult problem in the examination of many environmental samples. By utilizing the solution container as an electrochemical cell and employing the method of differential pulse anodic-stripping voltammetry at a hanging mercury drop electrode, it is shown that an automated read-out system in an enclosed environment can be developed for monitoring the solution-container interactions that occur over short or extended periods of time. In the present work, interactions of dilute solutions (1-10 mug/l.) of cadmium(II), lead(II), copper(II), zinc(II), and thallium(I) in glass, polyethylene and Teflon containers have been investigated at various pH values and in different ionic environments. The results demonstrate the importance of factors other than pH.     

Hydrodynamic voltammetry at tubular electrodes-III Determination of traces of bismuth by differential-pulse anodic-stripping voltammetry at a glassy-carbon tubular electrode with in situ mercury plating

An equation for the current in differential-pulse anodic-stripping voltammetry at tubular electrodes is derived. Application of a glassy-carbon tubular electrode to determination of traces of bismuth in environmental water samples by differential-pulse anodic-stripping voltammetry is described. In hydrochloric acid medium, the stripping peak current is proportional to the concentration of bismuth in the range 2-100 ng/ml, with a deposition time of 3-10 min. The detection limit is 0.5 ng/ml.     

Determination of tin in the presence of lead by stripping voltammetry with collection at a rotating mercury-film disc-ring electrode

Stripping voltammetry with collection at a rotating mercury-film disc-ring electrode is applied for the determination of tin in glassy-carbon methanolic hydrobromic acid solution. The limit of determination is 20 nM (2.3 ng ml^-1). Lead does not interfere when the lead/tin concentration ratio is less than ca. 500.     

Indirect determination of lutetium by differential pulse anodic stripping voltammetry at a hanging mercury drop electrode

Lutetium has been determined by differential pulse anodic stripping voltammetry in an acidic solution containing Zn-EDTA. Lutetium (III) ions liberated zinc (II), which was preconcentrated on a hanging mercury drop electrode and stripped anodically, resulting in peak current linearly dependent on lutetium (III) concentration. Less than 0.4 ng mL⁻¹ lutetium could be detected after a 2 min deposition.      

Analysis of domperidone in pharmaceutical formulations and wastewater by differential pulse voltammetry at a glassy-carbon electrode

The redox characteristics of the drug domperidone at a glassy-carbon electrode (GCE) in aqueous media were critically investigated by differential-pulse voltammetry (DPV) and cyclic voltammetry (CV). In Britton–Robinson (BR) buffer of pH 2.6–10.3, an irreversible and diffusion-controlled oxidation wave was developed. The dependence of the CV response of the developed anodic peak on the sweep rate (ν) and on depolizer concentration was typical of an electrode-coupled chemical reaction mechanism (EC) in which an irreversible first-order reaction is interposed between the charges. The values of the electron-transfer coefficient (α) involved in the rate-determining step calculated from the linear plots of E _p,a against ln (ν) in the pH range investigated were in the range 0.64 ± 0.05 confirming the irreversible nature of the oxidation peak. In BR buffer of pH 7.6–8.4, a well defined oxidation wave was developed and the plot of peak current height of the DPV against domperidone concentration at this peak potential was linear in the range 5.20 × 10⁻⁶ to 2.40 × 10⁻⁵ mol L⁻¹ with lower limits of detection (LOD) and quantitation (LOQ) of 6.1 × 10⁻⁷ and 9.1 × 10⁻⁷ mol L⁻¹, respectively. A relative standard deviation of 2.39% (n = 5) was obtained for 8.5 × 10⁻⁶ mol L⁻¹ of the drug. These DPV procedures were successfully used for analysis of domperidone in the pure form (98.2 ± 3.1%), dosage form (98.35 ± 2.9%), and in tap (97.0 ± 3.6%) and wastewater (95.0 ± 2.9%) samples. The method was validated by comparison with standard titrimetric and HPLC methods. Acceptable error of less than 3.3 % was also achieved. Figure In aqueous media at pH 7.6- 8.4, the DPV and cyclic voltammetry of the drug domperidone (I) at GCE showed an irreversible and diffusion controlled oxidation wave. The values of the electron transfer coefficient (α) involved in the rate determining step were found in the range 0.64± 0.05 confirming the irreversible nature of the peak. The analysis of the drug in pure form and in wastewater samples was successfully achieved     

Additive differential pulse voltammetry,instead of double differential pulse voltammetry

A new electrochemical double pulse potential technique called additive differential pulse voltammetry (ADPV) is proposed. This technique is inspired by the original idea of Birke et al. [Anal. Chem. 53 (1981) 852] of recording two differential pulse (DP) voltammograms and it consists of plotting the sum of these two signals versus the first pulse potential, although in this paper the proposal is to obtain the ADPV signal through just one experiment. ADPV behaves in an identical way to the triple-pulse technique double differential pulse voltammetry (DDPV) for reversible processes when diffusion coefficients are equal for spherical electrodes and for any value of diffusion coefficients in planar electrodes. In the case of reversible electrode processes with amalgamation of reaction product or other more complex processes, ADPV is more advantageous than DDPV. This is due, among other reasons, to the fact that, under these conditions, a double potential step is much simpler to analyse than a triple potential step.     

纳米银修饰电极差分脉冲伏安法测定盐酸金霉素

建立了快速测定盐酸金霉素(CTC)的方法。通过NaBH4还原法制备纳米银(AgNPs)溶胶,并利用X射线衍射和紫外-可见光谱进行表征。将制备好的AgNPs滴涂到玻碳电极表面制备修饰电极(AgNPs/GCE),研究了CTC在AgNPs/GCE上的电化学行为及伏安法测定,优化了缓冲溶液和pH等检测条件。结果表明,CTC在pH 3.3的柠檬酸-NaOH-HCl缓冲溶液中检测效果最佳。CTC在AgNPs/GCE上发生2个电子和2个质子的不可逆电化学氧化反应,且反应受吸附控制。最佳条件下,CTC的氧化峰电流与其浓度呈现良好的线性关系,线性范围为0.5~100μmol/L,检出限为0.14μmol/L。该修饰电极可用于河水样品检测。     

Determination of nanomolar concentrations of lead and cadmium by anodic-stripping voltammetry at the silver electrode

Lead and cadmium have been determined by subtractive anodic-stripping voltammetry (SASV) in the square-wave mode at a silver electrode without removal of oxygen. The sensitivities and detection limits for the two metals differ considerably. Detection limits of 0.05 nM for lead and 1 nM for cadmium have been achieved following 90 s electrodeposition. The repeatability of consecutive SASV runs is good (for lead 0.5% at 20 nM for 30 s electrolysis, 5% at 0.3 nM for 60 s electrolysis; for cadmium 2.5% at 20 nM for 30 s electrolysis, 5% at 5 nM for 60 s). Hundreds of runs can be carried out without any pretreatment of the electrode. The high stability is attributed to renewal of the electrode surface that takes place during the electrodeposition step in a two-electrode cell: the silver counter/quasi-reference electrode generates silver ions that codeposit with lead and cadmium at the Ag-RDE, thus ensuring a continuity of the latter. Underpotential deposition (UPD) plays a central role in anodic-stripping voltammetry (ASV). During the deposition step, the adatom coverage of trace elements is in the range of 0.01-1% and no bulk deposition is invoked for metals that exhibit UPD. The UPD properties and, as a result, the ASV signals are strongly affected by the type and concentration of the supporting electrolyte. The effects of Cl⁻, Br⁻, SO₄²⁻ and NO₃⁻ are shown. The analysis of lead and cadmium in natural waters has been performed. Surfactants distort the SASV signal. In order to ensure surfactant-free solutions, the samples were pretreated by wet ashing.     

Determination of trace metals by anodic-stripping voltammetry with a new kind of mercury electrode: The long-lasting sessile-drop electrode

A new kind of semi-stationary mercury drop electrode is described, which can be used for the determination of trace metals in natural waters by differential-pulse anodic-stripping voltammetry. Results are reported for the determination of zinc in potassium chloride and in samples of sea-water. The reproducibility of the electrode and of the results obtained with it for zinc at the 10(-8)M level are very satisfactory.     

Voltammetric determination of selenosulfate ions at a mercury-film electrode

A procedure is proposed for the voltammetric determination of selenium as selenosulfate (SO₃Se^2?) ions at a mercury-film electrode (MFE). Selenosulfate ions are determined in the range from 2 × 10^?4 to 1.0 × 10^?3 M without analyte accumulation, using peak current at ?0.92 ± 0.02 V and in the range from 1 × 10^?7 to 2 × 10^?4 M after analyte accumulation with the open circuit, using peak current at ?1.18 ± 0.03 V as the analytical signal. The mechanisms of SO₃Se^2? reduction at an MFE under the conditions of direct voltammetry and stripping voltammetry with accumulation are proposed and discussed.