Pulsed anodic stripping voltammetry of zinc,cadmium and lead with a mercury-coated wax-impregnated graphite electrode

The use of a thin mercury-film wax-impregnated graphite electrode for the simultaneous determination of cadmium, lead and zinc in an acetate buffer by differential pulse anodic stripping voltammetry is described. Optimal instrumental parameters for maximum resolution and sensitivity for simultaneous analysis of these three elements in natural waters are discussed. The interference of copper with the determination of zinc is investigated in detail. An optimal mercury film thickness for this electrode is suggested.     

Determination of trace metals by anodic stripping voltammetry using a bismuth-modified carbon nanotube electrode

A bismuth-modified carbon nanotube electrode (Bi-CNT electrode) was employed for the determination of trace lead, cadmium and zinc. Bismuth film was prepared by in situ plating of bismuth onto the screen-printed CNT electrode. Operational parameters such as preconcentration potential, bismuth concentration, preconcentration time and rotation speed during preconcentration were optimized for the purpose of determining trace metals in 0.1M acetate buffer solution (pH 4.5). The simultaneous determination of lead, cadmium and zinc was performed by square wave anodic stripping voltammetry. The Bi-CNT electrode presented well-defined, reproducible and sharp stripping signals. The peak current response increased linearly with the metal concentration in a range of 2-100 microg/L. The limit of detection was 1.3 microg/L for lead, 0.7 microg/L for cadmium and 12 microg/L for zinc (S/N=3). The Bi-CNT electrode was successfully applicable to analysis of trace metals in real environments.     

Application of gallium film electrode for elimination of copper interference in anodic stripping voltammetry of zinc

For elimination of copper interference in anodic stripping determinations of zinc at mercury and bismuth film electrodes gallium ions are usually added to the supporting electrolyte. In the presented studies novel ex situ formed gallium film electrode was applied for this purpose. The proposed electrode is less toxic than mercury one while the detection limit for zinc was lower than for bismuth film electrode following the same deposition time. The calibration graph for deposition time of 60 s was linear from 5 × 10⁻⁸ to 2 × 10⁻⁶ mol L⁻¹. The determinations of zinc were carried out from undeaerated solutions. The proposed procedure was applied to zinc determination in certified reference material and tap water sample.     

A novel tin-bismuth alloy electrode for anodic stripping voltammetric determination of zinc

We report on a novel tin-bismuth alloy electrode (SnBiE) for the determination of trace concentrations of zinc ions by square-wave anodic stripping voltammetry without deoxygenation. The SnBiE has the advantages of easy fabrication and low cost, and does not require a pre-treatment (in terms of modification) prior to measurements. A study on the potential window of the electrode revealed a high hydrogen overvoltage though a limited anodic range due to the oxidation of tin. The effects of pH value, accumulation potential, and accumulation time were optimized with respect to the determination of trace zinc(II) at pH 5.0. The response of the SnBiE to zinc(II) ion is linear in the 0.5–25?μM concentration range. The detection limit is 50?nM (after 60?s of accumulation). The SnBiE was applied to the determination of zinc(II) in wines and honeys, and the results were consistent with those of AAS.

Characterization and utilization of a long-lasting sessile-drop mercury electrode in differential pulse anodic-stripping voltammetric subtrace metal analysis of natural waters

Construction details and voltammetric characterization of a long-lasting sessile-drop mercury electrode are reported. The results obtained in the fully automated differential pulse anodicstripping voltammetric determination of cadmium in a simple purified electrolyte as well as of zinc, cadmium and lead in sea-water samples suggest that this new kind of semi-stationary mercury electrode may be employed in voltammetric trace and ultratrace analysis of natural waters for metal ions.     

Voltammetry using a dental amalgam electrode for heavy metal monitoring of wines and spirits

We have introduced a non-toxic electrode material similar to dental amalgam for use in voltammetry. Its electrochemical properties are like a silver electrode. However, it possesses a higher overvoltage towards hydrogen than silver, and therefore enables detection of metals like zinc, nickel and cobalt. As such solid electrodes are found to give stable results over several weeks, without any maintenance, and because this method greatly facilitates monitoring of heavy metals, attempts to apply such methods to various samples have been are carried out. The present paper deals with the determination of zinc and lead at nanogram per milliliter levels in wines and spirits with only minor treatment of the samples. The procedure may easily be adapted to continuous monitoring.We have previously found that audible sound may greatly increase the voltammetric signal using liquid mercury as well as silver as electrode material. This is also applied to the actual systems.Finally, model determinations of thallium in brandy with the dental amalgam electrode are compared with atomic absorption spectrometric (AAS) measurements. It was found that the electrode could be used repeatedly, without fouling, and with results close to those found by the AAS method.     

The use of the rotated dropping mercury electrode in polarographic analyses and amperometric titrations of micromolar solution

The applicability of the rotated dropping mercury electrode in conventional direct current polarography, alternate current polarography, and amperometric titrations, has been investigated. The direct current polarographic method was applied to the determination of minute quantities of lead contained in high-purity electrolytic zinc, the lowest content of lead determined being 0.0001 %. It was confirmed that the rotation of the electrode has no advantage in alternating current polarography. Some characteristics of the electrode, revealed by the measurement of current-time curves, are also presented and discussed.     

Novel sulfate ion-selective polymeric membrane electrode based on a derivative of pyrilium perchlorate

A sulfate ion-selective PVC membrane sensor based on 4-(4-bromophenyl)-2,6-diphenylpyrilium perchlorate (BDPP) as a novel sensing material is successfully developed. The electrode shows a good selectivity for sulfate ion with respect to common organic and inorganic anions. The sensor exhibits a good linear response with slope of -28.9+/-0.5 mV per decade over the concentration range of 1.0x10(-6)-1.0x10(-2) M, and a detection limit of 8.0x10(-7) M of SO(4)(2-) ions. The electrode response is independent of pH in the range of 4.0-9.0. The proposed sensor was applied as an indicator electrode in potentiometric titration of sulfate and barium ions, and to the determination of zinc in zinc sulfate tablets.     

Investigation of materials for making a carbon-support zinc-selective electrode

The usefulness of zinc orthophosphate and zinc mercuric thiocyanate to make a carbon-support electrode responsive to zinc was investigated. The best results were obtained with zinc orthophosphate, which produced a Nernstian response to zinc in the concentration range from 10(-5) to 10(-2)M. The electrode response was lowered by the formation of acidic oxides on the surface of the electrode. Different ways of minimizing this problem are discussed. Interference effects from copper(II) (K(pot)(Zn.Cu) = 1.0), cadmium (K(pot)(Zn.Cd) = 8.9) and lead (K(pot)(Zn.Pb) = 10) were observed.     

Differential pulse voltammetry with fast pulse repetition times in a flow-injection system with a copper-amalgam electrode

The reductive determination of cadmium and zinc is used to illustrate the effects of pulse repetition times in differential pulse voltammetry at solid electrodes. With 100-ms repetition times, signal-to-background ratio is shown to improve in flow-injection response studies at a copper-amalgam working electrode for both voltage scanning and amperometric operation, allowing scan rates up to 100 mV s^?1, and detection limits of 0.07–0.15 ng for cadmium and zinc after deaeration of sample solutions. Peak widths at baseline in the range 12–30 s, depending on flow rate, are obtained in the flow-injection system for cadmium and zinc at working potentials of ?0.77 and ?1.27 V, respectively. Interferences occur when cadmium is in large excess over zinc, although the voltammetric peaks do not overlap.     

Sulfate-selective PVC membrane electrode based on a strontium Schiff's base complex

A strontium Schiff's base complex (SS) can be used as a suitable ionophore to prepare a sulfate-selective PVC-based membrane electrode. The use of oleic acid (OA) and hexadecyltrimethylammonium bromide (HTAB), as additives, and nitrobenzen (NB), dibutyl phthalate (DBP) and benzyl acetate (BA) as solvent mediators, were investigated. The best performance was observed with a membrane composition PVC: NB: SS: HTAB of 30%: 62%: 5%: 3% ratio. The resulting sensor works well over a wide concentration range (1.0 x 10(-2)-1.0 x 10(-6) M) with a Nernstian slope of -29.2 mV per decade of sulfate activity over a pH range 4.0-7.0. The limit of detection of the electrode is 5 x 10(-7) M. The proposed sensor shows excellent discriminating ability toward SO4(2-) ions with regard to many anions. It has a fast response time of about 15 s. The membrane electrode was used to the determination of zinc in zinc sulfate tablets. The sensor was also used as an indicator electrode in the potentiometric titration of SO4(2-) against barium ion.     

The polished precipitate electrode: A new voltammetric method with the solid electrode

A new surface-renewal technique at the solid electrode has been developed, based on continuous polishing. Well-defined and reproducible current-voltage curves similar to those obtained in polarography are given by the "polished precipitate electrode" (PPE). The method can be used for the continuous determination of electroactive substances and for the study of electrode reaction mechanisms at the solid-liquid interface.     

多壁碳纳米管修饰电极阳极溶出法测定痕量锌

报道了自制的多壁碳纳米管修饰电极测定锌离子的电分析方法。在浓度0.20mol/L的乙酸钠溶液中,以此修饰电极作为工作电极,以-1.50V为富集电位,150s为富集时间,用方波伏安溶出法(起始电位:-1.5V;终止电位:-0.8V;电位增量:0.01V;振幅:0.05V;频率:5Hz)测定-1.30V处的峰电流,用峰高定量。结果表明,该电极对锌离子吸附的灵敏度较高;当锌离子浓度为1.0×10-6～9.0×10-6mol/L时,线性关系好,相关系数为0.9992;对自来水样本进行了测定,取得了满意的结果,加标回收率在97%～105%之间。     

用于非水介质分析的新型离子选择电极: 水膜电极的设想及验证

本文首次提出了一种新型离子选择电极—水膜电极, 采用水溶液作为液膜, 可分析有机溶液中的组分. 这种电极用于非水介质中的分析 , 有其独特的优点, 可直接测量非水溶液中某种离子的平衡活度(或浓度), 对理论研究有较大的意义. 本文提出的水膜电极能应用于不与水相混溶的低介电常数有机溶剂, 扩展了离子选择电极在非水介质中的研究与应用.     

锌电极在氢氧化钾溶液中阳极惰化时的表面相变的研究

本文试图进一步从动力学方面证明恒电位下的锌电极在KOH溶液中阳极惰化时,阳极溶解电流随时间而缓慢下降是由于“表面相变”所引起。用恒电位法测取了锌电极在不同浓度的KOH溶液中电流对时间的曲线。实验结果与推导的动力学方程式相符,表明在恒电位惰化条件下,锌电极表面上最初形成的[Zn(OH)_2]_(ad)在OH~-参预下徐缓地转变为较不易溶的[ZnO]_(ad),因而导致阳极溶解电流的下降。这一表面相变过程可表示如下:     

Determination of concentrated hydrogen peroxide at single-walled carbon nanohorn paste electrode

Single-walled carbon nanohorn (SWCNH) paste electrode was used for amperometric determination of concentrated hydrogen peroxide, and was compared with other carbon electrodes. The calibration plots are linear from 0.5 to 100 mM at activated SWCNH paste electrode and edge plane graphite (EPG) electrode. In contrast, the calibration plots are linear only at concentrations lower than 45 mM at graphite paste electrode, multi-walled carbon nanotube paste electrode, and glassy carbon electrode. Our results show that SWCNH paste electrode and EPG electrode are interesting alternatives to high surface area platinum electrode for determination of concentrated hydrogen peroxide. Because of its high-purity, metal-free SWCNH is a user-friendly and attractive material for electrochemical study.     

Application of the cap-pair effect in reducing the inhibition of electrode processes. The determination of zinc in the presence of tween-80

The “cap-pair” effect, which accelerates electrode processes, is shown to be useful in decreasing the effects of inhibitors on reduction processes. The determination of zinc in the presence of Tween-80 is used as an example. In the square-wave polarography of zinc at the 10^-5 M level, addition of thiourea (10 g l^-1) eliminates or greatly reduces the inhibitory action of Tween-80, thus allowing precise determinations.     

A bromide selective polymeric membrane electrode based on Zn(II) macrocyclic complex

A novel bromide ion-selective PVC membrane sensor based on 2,3,10,11-tetraphenyl-1,4,9,12-tetraazacyclohexadeca-1,3,9,11-tetraene zinc(II)complex (I) as carrier has been developed. The electrode exhibited wide working concentration range 2.2 × 10⁻⁶ to 1.0 × 10⁻¹ M and a limit of detection as 1.4 × 10⁻⁶ M with a Nernstian slope of 59.2 ± 0.5 mV per decade. The response time of electrode was 20 s over entire concentration range. The electrode possesses the advantages of low resistance, fast response and good selectivities for bromide over a variety of other anions and could be used in a pH range of 3.5–9.5. It was successfully used as an indicator electrode in the potentiometric titration of bromide ions with silver ion and also in the determination of bromide in real samples.     

Dual electrode electrochemical detector for HPLC

Summary A method for determination of phenolic compounds in distilled alcoholic beverages has been developed. After separation by reversed phase chromatography these compounds are detected coulometrically in a dual electrode detector. The hydrodynamic electrochemical behaviour of the substances in oxidative and reductive mode was investigated. For quantitative determination phenolic compounds are oxidized at the first working electrode (+0.65 V); then the oxidation products are reduced at the second working electrode (0.0 V). The current due to these processes is recorded. By the high selectivity of the detection mode matrix interferences can be eliminated in several alcoholic beverages. In this way qualitative information is improved. The detection limits of phenolic acids and aldehydes are between 0.01 and 1 ng (S/N=3).

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Dualelektroden-Detektor für die HPLCBestimmung von phenolischen Verbindungen in Spirituosen

     

固态碳糊电极电位法测定利多卡因注射液

本文报道了一种以利多卡因与单质碘形成的缔合物为电活性物的全固态碳糊利多卡因电极,电极的线性响应范围5.0×10-2～4.0×10-5mol.L-1,级差电位为30mV/pC,检测下限为3.0×10-5mol.L-1。该电极响应迅速,重现性好,用该电极测定了盐酸利多卡因注射液中利多卡因的含量,结果与药典法相符。