Voltammetric behavior of benzo[a]pyrene at boron-doped diamond electrode: a study of its determination by adsorptive transfer stripping voltammetry based on the enhancement effect of anionic surfactant, sodium dodecylsulfate

Benzo[a]pyrene (BaP), a member of the polycyclic aromatic hydrocarbon (PAH) class, is one of the most potent PAH carcinogens. The electrochemical oxidation of BaP was first studied by cyclic voltammetry at the boron-doped diamond electrode in non-aqueous solvent (dimethylsulphoxide with lithium perchlorate). The compound was irreversibly oxidized in a single step at high positive potential, resulting in the well-resolved formation of a couple with a reduction and re-oxidation wave at much lower potentials. Special attention was given to the use of adsorptive stripping voltammetry together with a medium exchange procedure in aqueous and aqueous/surfactant solutions over the pH range of 2.0-8.0. The technique in aqueous solutions had little value in practice because of too small oxidation peak current. This problem was solved when surfactants were added into the sample solution, by which the oxidation peak currents of BaP were found enhanced dramatically. The employed surfactants were sodium dodecylsulfate (anionic, SDS), cetyltrimethylammonium bromide (cationic, CTAB) and Tween 80 (non-ionic). Using square-wave stripping mode, the compound yielded a well-defined voltammetric response in Britton-Robinson buffer, pH 2.0 containing 2.5 × 10⁻⁴ M SDS at +1.07 V (vs. Ag/AgCl) (after 120 s accumulation at +0.10 V). The process could be used to determine BaP in the concentration range of 16-200 nM (4.04-50.46 ng mL⁻¹), with a detection limit of 2.86 nM (0.72 ng mL⁻¹). This method was also applied to determine BaP in model water sample prepared by adding its different concentrations into tap water.     

利用钛保护层在ITO电极上直接制备大面积的超薄氧化铝膜

通过磁控溅射并引入钛保护层, 利用在0.3 mol·L^-1硫酸中20 V电压下二次阳极氧化, 在氧化铟锡(ITO)导电玻璃衬底上直接制备了超薄(约140 nm, 为阳极氧化前Al厚度的一半)、大面积(约4 cm²)的多孔阳极氧化铝(AAO). 扫描电子显微镜结果表明生成的微孔与衬底垂直, 孔径和孔间距分别约为30和60 nm. 我们发现钛保护层的作用是提高了Al层的附着性并且防止ITO被腐蚀, 在此体系中钛不能被其它的金属如铬、金、银或铜代替. 紫外-可见光谱透过率结果显示在阳极氧化过程中Ti被氧化成为透明的TiO₂, 利用10-20 nm的钛保护层以及二次阳极氧化过程, 能够保证高透明度. 在ITO上直接制备的这种透明、有序的AAO纳米结构在光子学、光伏领域和纳米制备等方面具有潜在应用.     

Preconcentration and Determination of Copper(II) at a Chemically Modified Electrode Containing Salicylaldehyde Thiosemicarbazone

A chemically modified electrode (CME) containing salicylaldehyde thiosemicarbazone (TSCsal) was evaluated for the ability to preconcentrate copper(II) prior to quantification by voltammetry. The CME has been used for the very sensitive and selective analysis of trace amounts of copper(II). A detection limit of 0.1 ppb was obtained by applying anodic stripping voltammetry with a flow system. The parameters that affect the sensitivity and possible interference by other ions or chelating agents have been examined in detail. The CME exhibits high stability and the response could be reproduced for four preconcentration-determination-renewal cycles [10ppbCu(II)] with a 2.87% relative standard deviation. The proposed method has been applied to the determination of copper(II) in tap water, drinking water, and NASS-3 standard reference sea water samples. The results gave satisfactory recoveries.     

DPASV Method for Determination of Trace Concentrations of Manganese in Non-Buffered Chloride Solutions by Addition of Cyanide as a Masking Agent

 A highly sensitive, selective, and rapid differential pulse anodic stripping voltammetric method at HMDE is described for the determination of trace concentrations of Mn²⁺. The determination of Mn²⁺ in non-buffered chloride solution is seriously disturbed by the presence of Ni²⁺, Co²⁺, Cr³⁺, Zn²⁺ and Cu²⁺ due to intermetallic compound formation. The procedure is based on the addition of low amounts of cyanide as a masking agent. The interference of < 20 μgL⁻¹ of Ni²⁺, Co²⁺ and Cr³⁺ and < 75 μgL⁻¹ of Cu²⁺ and Zn²⁺ can thus be avoided, as the formed cyanide complexes prevent intermetallic compound formation during the short accumulation period. Thus, the addition of cyanide greatly improves the DPASV determination of manganese in non-buffered medium. A comparison between the determination of Mn²⁺ in the presence of a mixed cyanide/non-buffered chloride and in the ammoniacal buffer solution shows that the peak current of manganese in the presence of cyanide is four times higher with the same peak potential. The proposed method is shown to be applicable for the Mn²⁺ determination in both ground and tap water. A good agreement is obtained between the results by DPASV and AAS. Received May 14, 1999. Revision May 25, 2000.     

Ultra‐sensitive Voltammetric Aluminum Determination on a Solid Bismuth Electrode for Water Filter Verification

This work presents a new ultra‐sensitive method of Al(III) as Al‐cupferron complex voltammetric determination, in 0.04 M ammonium sulfate of pH=6.1 and 0.003 M cupferron by environmentally friendly and durable Bismuth Bulk Annular Band Electrode (BiABE). The optimal measuring parameters include: potential window from ?700 to ?1250 mV versus Ag|AgCl, preconcentration time and potential of 120 s, ?700 mV, respectively. The electrode surface can be activated by fast in situ method: applying short conditioning by the potential of ?1300 mV. The best obtained analytical parameters are: range of linearity 0.2–1.2 μg L^?1 with high sensitivity of 1.333 μA/μg L^?1, limit of detection 0.04 μg L^?1 and repeatability below 2.3 %. The described procedure was verified using various CRMs, i. e. surface waters, waste waters and tea leaves. Satisfactory recovery values were obtained in the interval 99.2–103.5 %. Developed DPV procedure was used to determine Al in tap and natural waters in aspect of recovery of aluminum, which was added to the samples. For the first time, we tested also Al removal efficiency from water by the water filters mounted in the trip bottle.     

Effect of Sb on the properties of anodic Pb(Ⅱ) oxide film formed in alkaline solution

The composition and properties of the anodic films formed on Pb and Pb-3at.%Sb alloy at -0.10 V (vs. Hg/HgO) for 2.5 h in 0.1 mol.dm-3 NaOH solution (25℃) were investigated by cyclic voltammetry, linear sweep voltammetry, open circuit decay curve, photocurrent technique, X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that the anodic film formed oh Pb mainly consists of t-PbO, while that on Pb-3at.%Sb consists of o-PbO, t-PbO and a small amount of orthorhombic Sb2O3. The dominant component of the film anodically grown on Pb-3at.%Sb for less than 5 min is o-PbO, however, t-PbO is the major component of the anodic film formed for 1 h or longer. It is established that Sb suppresses the growth of t-PbO. The anodic film formed on Pb-3at.%Sb is less porous than that on Pb. The bandgap energies of t-PbO and o-PbO in the films were determined by photocurrent measurements to be 1.83-1.84 eV and 2.60 eV, respectively.     

Anodic oxidation of chiral sulfinylamines: a new route to highly diastereoselective α-alkylation of piperidine

The anodic oxidation of some chiral non-racemic N-arylsulfinyl piperidines was investigated and for the first time α methoxylated sulfinyl piperidines were obtained. The so-formed compounds are equivalent of chiral N-sulfinyliminiums and used as new intermediates for the preparation of chiral α-substituted piperidine derivatives in good yield and diastereoselectivity.     

The effects of anodic and cathodic processes on the characteristics of ceramic coatings formed on titanium alloy through the MAO coating technology

This paper reports on the investigation into the effects of the different anodic j_a and cathodic j_c current densities on the variations of the anodic and cathodic processes and the associated changes in the characteristics of the coatings synthesized on Ti-6Al-4V alloy substrate by microarc oxidation technique. The coated samples were subjected to coating thickness and cross-section fracture observation. Phase and elemental composition at different depth of the coatings were evaluated through X-ray diffraction and energy dispersive spectrum analyses. The experimental results indicate that the increase of j_a leads to the increasing slope of anodic voltage U₊ versus oxidation time plots, the larger coating thickness and the more coarse surface morphology of MAO coatings; while the aggrandizement of the cathodic process results in the lower growth rate and more uniform structure of coatings. The changes of the elements distribution from the interface towards the coating surface with variation of j_a and j_c are affected by the Ti anodic dissolution and the electromigration of electriferous particles, such as Al(OH)₄⁻, in electrolytes.     

碱性介质中葡萄糖在铂电极上的阳极氧化

为了进一步探明葡萄糖在铂电极上的氧化机理 ,用循环伏安法 (CV)在 - 0 .9～ 0 .4V(相对于饱和甘汞参比电极 )内研究了葡萄糖在铂电极上催化氧化行为 ,首次详细报道了葡萄糖在电化学氧化过程中的电位振荡现象 ,并用电流扫描法表征了葡萄糖的电位振荡情况 .电流扫描结果表明 ,在较慢的电流扫描速度下 ,电极过程出现了明显的电位振荡 .说明电极上产生了毒化中间物 ,电位振荡是由于毒化中间物在电极上的吸附和在高电位下氧化除去引起的 .     

Single-step microwave digestion of food and biological samples for the quantitative conversion of Se into the +4 oxidation state

An improved single step microwave digestion procedure is described for providing the fast and easy exhaustive mineralisation of biological samples concomitantly with the quantitative conversion of any type of selenium compounds into Se(IV). In such a way, digested samples are directly suitable for the subsequent Se analysis at trace and ultratrace levels by both spectrometric methods such as HG-ICP-MS or HG-ICP-OES and differential pulse cathodic stripping voltammetry (DPCSV). It is based on the use, under suitably optimised microwave irradiation conditions, of a digestion mixture with a carefully tailored composition such that its redox potential is made lower than that allowing Se(IV) to be oxidized to Se(VI), but high enough to permit total destruction of biological or, in general, organic matrices. It consists of a nitric acid (65%, w/w) and hydrogen peroxide (30%, w/w) mixture in a volume ratio 5:1, frequently adopted for the mineralisation of organic and biological samples, but added simply with 0.25 g mL⁻¹ of NaCl. Successful application of the procedure, in terms of both repeatability and accuracy, to the quantification of selenium by the instrumental methods above in standard compounds and in a certified biological sample proved its good performance. The application to the Se determination in human blood plasma and in a wide variety of foods is also reported.