Subspeciation of sulfidic nickel in particulates. Determination of Ni3S2, NiS2, and NiS in reference and fly ash samples by carbon paste electrode voltammetry

Nickel speciation of fly ash by sequential extraction lacks specific identification of the chemical forms in the sulfidic nickel phase. A new voltammetric analysis of Ni₃S₂, NiS, and NiS₂ in a carbon paste electrode is reported. Characteristic peaks were observed in acetate (pH 5) as the electrolyte; the anodic peak for Ni₃S₂ gave a linear dose response with microgram sensitivity. Reference compounds included heazlewoodite, millerite, commercial Ni₃S₂, NiS₂, and NiS, but the latter was shown to be mainly the subsulfide. No Ni₃S₂ was found in two types of laboratory generated ash: an oil ash containing mainly soluble nickel and a high sulfur petroleum coke ash enriched with nickel.     

Subspeciation of nickel disulfide by carbon paste electrode voltammetry catalyzed by Ni2+

In subspeciation of sulfidic nickel, carbon paste electrode voltammetry was developed for the specific determination of Ni3S2 or NiS, but NiS2 was found to be unreactive. Ni2+ in pH 7.2 acetate solution was able to catalyze NiS2 to undergo redox reactions. The cyclic voltammogram showed two anodic peaks at -0.3 and +0.7 V and a cathodic peak at -0.6 V. The first anodic peak at -0.3 V and the cathodic peak were common among the three nickel sulfides, but the second anodic peak at +0.7 V was unique to NiS2. This peak current gave a linear dose response to NiS2 from 40 to 610 microg, with a correlation coefficient of 0.994, and a detection limit of 40 microg.     

Subspeciation of nickel disulfide by carbon paste electrode voltammetry catalyzed by Ni2+

In subspeciation of sulfidic nickel, carbon paste electrode voltammetry was developed for the specific determination of Ni₃S₂ or NiS, but NiS₂ was found to be unreactive. Ni²⁺ in pH 7.2 acetate solution was able to catalyze NiS₂ to undergo redox reactions. The cyclic voltammogram showed two anodic peaks at –0.3 and +0.7 V and a cathodic peak at –0.6 V. The first anodic peak at –0.3 V and the cathodic peak were common among the three nickel sulfides, but the second anodic peak at +0.7 V was unique to NiS₂. This peak current gave a linear dose response to NiS₂ from 40 to 610 μg, with a correlation coefficient of 0.994, and a detection limit of 40 μg.     

Determination of nickel by anodic adsorptive stripping voltammetry with a cation exchanger-modified carbon paste electrode

The behavior of a modified carbon paste electrode (CPE) for nickel determination by anodic adsorptive stripping voltammetry (AAdsSV) was studied. The electrode was built incorporating the Dowex 50W x 12 (H(+) form) ion exchanger to a Nujol-graphite base paste. Ni(2+) was preconcentrated on the electrode surface in open circuit conditions, with the reduction (-1300 mV)/reoxidation step carried out in HCl solution (pH 3). During deposition time (5 min), the hydrogen evolution did not present obstacle in the quantification of nickel. For 12 min of accumulation and 5 min of deposition, nickel can be quantified up to 600 mug l(-1). The detection limit was 0.005 mug l(-1) at a linear potential scan rate of 200 mV s(-1). Interferences from Hg(2+) and Ag(2+) up to a concentration of 1 and 0.6 mg l(-1), respectively, were eliminated with the aid of the anion exchanger Dowex-2 (mesh 200-400) which was added to the sample in the preconcentration step. The tolerance for some metal ions such as Cu(2+), Cd(2+), Fe(3+), Zn(2+), Co(2+) and Pb(2+) was improved in the same way. The method was applied for the determination of nickel in samples of tap and mineral water. At the concentration level of 50 mug l(-1) of Ni (2+), the results were in good agreement with those obtained using Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). For a Ni(2+) concentration of 5 mug l(-1), the results obtained showed better accuracy than those obtained by ICP-AES.     

碳糊电极阳极吸附伏安法测定洛美沙星

报道了碳糊电极阳极吸附伏安法测定洛美沙星的新方法。在0.096mol L的KHP NaOH(pH5.4)缓冲液中,用碳糊电极为工作电极,在0.3V(vs.SCE)富集一定时间,然后从0.3～1 3V以300mV s扫速线性扫描,记录其在1 02V的二次导数阳极溶出峰。溶出峰电流与洛美沙星浓度在8.0×10-9～8.0×10-8mol L(富集90s)和8.0×10-8～8.0×10-7mol L(富集30s)范围内呈良好的线性关系,相关系数分别为0.9844和0.9967,检出限为9.0×10-10mol L(S N=3)。探讨了洛美沙星在碳糊电极上的伏安性质和电极反应机理,并且成功地应用于人体尿液中洛美沙星的测定,结果与紫外光度法基本吻合。     

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.

---

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

     

碳糊电极阳极吸附伏安法测定吡哌酸

吡哌酸（Pipmidic acid,简称PPA）,是吡喹酮类合成抗菌药物,目前的主要分析方法有分光光度法、交流示波滴定法、高效液相色谱法、阴极吸附溶出伏安法、单扫描示波极谱法、微分脉冲极谱法和循环伏安法。本文提出了在CPE上阳极吸附伏安法测定PPA的方法,并探讨了PPA在CPE上的伏安性质和电极反应机理。该法准确、简便、灵敏度高,应用于模拟尿样中痕量PPA的测定,得到满意的结果。     

Adsorptive stripping voltammetry of nickel at a bare glassy carbon electrode

A bare glassy carbon electrode is applied to nickel determination by adsorptive stripping voltammetry in the presence of dimethylglyoxime as a complexing agent. A procedure of nickel determination and electrode regeneration was proposed. The calibration graph for Ni(II) for an accumulation time of 120?s was linear from 2?×?10^?9 to 1?×?10^?7?mol?L^?1. The detection limit was 8.2?×?10^?10?mol?L^?1. The relative standard deviation for a solution containing 2?×?10^?8?mol?L^?1 of Ni(II) was 4.1%. The proposed procedure was applied for Ni(II) determination in certified water reference materials.     

碳糊修饰电极吸附伏安法测定食品中的锑

研制了溴邻苯三酚红 (BPR)作修饰剂的碳糊修饰电极 ,并用此电极作工作电极建立了测定痕量锑的吸附伏安法。在选定的实验条件下 ,峰电流与Sb(Ⅲ )浓度在 8.0× 1 0 -9～ 2 .0× 1 0 -7mol L范围内呈线性关系 ,检出限为 2 .0×1 0 -9mol L ,1 0次测定相对标准偏差为 2 .0 % ,不用分离 ,可直接测定食品中痕量Sb(Ⅲ ) ,测定的回收率为 90 %～ 1 0 3%。     

Adsorption voltammetry of the scandium-alizarin red S complex onto a carbon paste electrode

For the first time, a new method is described for the determination of scandium based on the cathodic adsorptive stripping of the scandium-alizarin red S complex onto a carbon paste electrode. The second-order derivative linear scan voltammograms of the complex are recorded by use of model JP-303 polarographic analyzer from 0.0 to -1.0 V (versus SCE). Optimum conditions are found to be: an acetic acid (0.36 mol l(-1))-potassium biphthalate (0.064 mol l(-1)) buffer solution (pH 4.0) containing 2.0x10(-5) mol l(-1) alizarin red S, a preconcentration potential of 0.0 V, a preconcentration time of 60 s, a rest time of 10 s and a scan rate of 100 mV s(-1). The results show that the complex can be adsorbed on the surface of a carbon paste electrode, yielding one peak at -0.58 V, corresponding to the reduction of alizarin red S in the complex at the electrode. The detection limit is found to be 6.0x10(-10) mol l(-1) for 3 min of preconcentration time. The linear range is 1.0x10(-9) to 4.0x10(-7) mol l(-1). Application of the procedure to the determination of scandium in the ore samples gave good results.     

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.     

Detection of dopamine in the pharmacy with a carbon nanotube paste electrode using voltammetry

A simply prepared DNA immobilized on a carbon nanotube paste electrode (CNTPE) was utilized to monitor dopamine ion concentration using the cyclic voltammetry (CV) and square-wave (SW) stripping voltammetry methods. The optimum analytical conditions were sought. The result obtained was a very low detection limit compared to other common voltammetry methods. The optimal parameters were found to be as follows: 3.5 pH, 0.48 V SW amplitude, 71 Hz frequency, 5 s accumulation time, 0.01 V increment potential, and -1.3 V (anodic-*-) and 1.2 V (cathodic-o-) accumulation potentials. Given these conditions, the linear working range was observed to be within 0.01-0.11 microg L(-1) (SW anodic and CV). The analytical detection limit was determined to be SW anodic and CV: 4.0 microg L(-1) (2.1 x 10(-11) mol L(-1)) dopamin, and the relative standard deviation at the dopamine concentration of SW anodic 0.05 microg L(-1) was 0.02% (n=15) at the optimum conditions.     

Study on the adsorptive catalytic voltammetry of aloe-emodin at a carbon paste electrode

Recently, the studies and applications for the pola-rographic catalytic waves of organic compounds at dropping mercury electrode made considerable head-way. Tovopova et al.[1―4] reported the polarographic catalytic waves of the organic compounds containi…     

Determination of copper ion by square wave anodic stripping voltammetry at antimony trioxide-modified carbon nanotube paste electrode

In this work, an antimony trioxide-modified multi-walled carbon nanotube paste electrode (Sb₂O₃/CNTPE) was employed for determination of Cu²⁺ ions by using square wave anodic stripping voltammetry (SWASV) in the presence of 8-hydroxy-7-iodo-5-quinoline sulfonic acid (HIQSA) as a chelating agent. The field emission scanning electron microscopy (FE-SEM), energy-dispersive spectroscopy (EDS) and electrochemical impedance spectroscopy (EIS) methods were applied to estimate the morphology and properties of the modified electrode. Measurements related to SWASV were taken in 0.6 M HCl at ?1.0 V versus Ag|AgCl|KCl (3 M) for 90 s (deposition step). After equilibrium time of 15 s, an ASV appeared at 0.0 V versus Ag|AgCl|KCl (3 M) (stripping step). The sensor depicted a fairly linear response for Cu²⁺ in the concentration range of 2–100 ppb with appropriate detection limit about 0.39 ppb and limit of quantification about 1.3 ppb. The stability of the modified electrode during 7 weeks and its behavior in the presence of some metal ions was evaluated. The practical applicability of the Sb₂O₃/CNTPE was established on the voltammetric determination of Cu²⁺ in tap water as a sample.     

Electrochemical liquid-phase microextraction and determination of iodide in kelp based on a carbon paste electrode by cyclic voltammetry

We describe the coupling of liquid-phase microextraction (LPME) with cyclic voltammetry for the determination of iodine in kelp based on a carbon paste electrode with a mixture of castor oil and ethyl benzoate as the organic binder and extracting agent. The iodide was quickly adsorbed on the micro-liquid membrane covering a graphite powder surface without the influence of an applied potential. The extraction follows a Freundlich adsorption isotherm. The oxidation peak current was proportional to the exponential function of iodide concentration in the range from 10 to 400 μM. The method is sensitive, selective, simple, convenient, not interfered by chloride or bromide, and was applied to the determination of iodide in kelp with a recovery of 99.0–119.7%.     

钡离子在玫红酸钠修饰碳糊电极上电化学固相微萃取研究

本文以电化学活性的玫红酸钠修饰碳糊电极,利用玫红酸盐与钡离子的络合效应,实现钡离子的电化学固相微萃取。以循环伏安法研究了钡离子的固相微萃取及其最佳实验条件。固相微萃取的动力学符合S形曲线模型,获得表观一级反应速率常数为2.183 min-1。固相微萃取的热力学遵循Freundlich等温吸附模型,吸附常数为n=11.4,k=1.025。     

Adsorption voltammetry of the zirconium-alizarin red S complex at a multi-walled carbon nanotubes modified carbon paste electrode

We used a carbon paste electrode modified with multi-walled carbon nanotubes as a working electrode and studied the electrochemical behavior of zirconium-alizarin red S complex on it. It was found that the modified electrode exhibited a significant catalytic effect toward the reduction of free alizarin red S and the complex. The second derivative linear scan voltammograms of the complex were recorded by a polarographic analyser from 0 to −1000 mV (vs. SCE), and it was found that the complex can be adsorbed on the surface of the modified electrode, yielding a peak at about −470 mV, corresponding to the reduction of alizarin red S in the complex. The linear range was found to be 2.0 × 10⁻¹¹–8.0 × 10⁻⁷ mol L⁻¹, and the detection limit was 1.0 × 10⁻¹¹ mol L⁻¹ (S/N = 3) for 3 min accumulation. The procedure was successfully applied to the determination of trace amounts of zirconium in the ore samples. Correspondence: Pei-Hong Deng, Department of Chemistry and Material Science, Hengyang Normal University, Hengyang Hunan 421008, P.R. China     

Enzyme-free ethanol sensor based on electrospun nickel nanoparticle-loaded carbon fiber paste electrode

We have developed a novel nickel nanoparticle-loaded carbon fiber paste (NiCFP) electrode for enzyme-free determination of ethanol. An electrospinning technique was used to prepare the NiCF composite with large amounts of spherical nanoparticles firmly embedded in carbon fibers (CF). In application to electroanalysis of ethanol, the NiCFP electrode exhibited high amperometric response and good operational stability. The calibration curve was linear up to 87.5 mM with a detection limit of 0.25 mM, which is superior to that obtained with other transition metal based electrodes. For detection of ethanol present in liquor samples, the values obtained with the NiCFP electrode were in agreement with the ones declared on the label. The attractive analytical performance and simple preparation method make this novel material promising for the development of effective enzyme-free sensors.