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.     

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.     

次黄嘌呤在铜电极上的伏安特性研究

研究了次黄嘌呤（Ｈｘａ）在铜电极上的电化学行为．实验发现，以１．９６×１０－３～４×１０－４ｍｏｌ·Ｌ－１ＮａＯＨ作支持电解质时，在－０．２５～－０．４０Ｖ的电位范围内有一灵敏的阴极峰，它是吸附于铜电极表面的Ｈｘａ与Ｃｕ＋络合物的溶出伏安峰．在选择的实验条件下，峰高与Ｈｘａ的浓度在１．４６×１０－６～２×１０－３ｍｏｌ·Ｌ－１范围内呈良好的线性关系，最低检测限为５．６×１０－８ｍｏｌ·Ｌ－１，可用于痕量的Ｈｘａ的检测．     

Accurate determination of the CO coverage at saturation on a cyanide-modified Pt(1 1 1) electrode in cyanide-free 0.5 M H2SO4

We have used the CO charge-displacement method, in combination with a thermodynamic cycle, to obtain the double-layer correction necessary to determine accurately, using the charge in the corresponding CO-stripping voltammograms, the maximum amount of CO that can adsorb on a cyanide-modified Pt(1 1 1) electrode. The resulting CO coverage at saturation is θ_CO=0.25, and corresponds to a mixed CN–CO adlayer where some Pt atoms are still free and consequently can adsorb hydrogen. The hydrogen adsorption charge for the mixed adlayer, obtained from the corresponding cyclic voltammogram, agrees very well with that estimated from the CO and CN coverages, assuming that one hydrogen atom adsorbs on every free Pt atom. Taking into account these data, we propose a structural model for the mixed CN–CO adlayer on Pt(1 1 1).     

Rapid evaluation of the rechargeability of c-MnO2 in alkaline media by abrasive stripping voltammetry

Cyclic abrasive stripping voltammetry is shown to provide the experimental basis for the evaluation of the rechargeability of γ-MnO₂ in 9 M KOH. Relative discharge capacities at different depths of discharge (DOD) with respect to the first one-electron reduction of γ-MnO₂ are compared when metal ions such as Ba²⁺ or Zn²⁺ are additionally present in the electrolyte solution. At about 30% DOD, resulting relative discharge capacities are essentially equal to those of AA cells either in the absence or presence of Ba²⁺ ions from about 10 discharge/charge cycles. However, the corresponding time scales are substantially different. While it takes about 2.7 h to complete 20 discharge/charge cycles in the case of abrasive stripping voltammetric characterization, some 360 h are needed to cycle an AA-sized battery in the conventional manner. Received: 25 November 1997 / Accepted: 20 January 1998     

Wall pressure and shear stress measurements beneath an impinging jet

This paper presents comprehensive measurements of wall pressure and surface shear stress beneath a plane, two-dimensional, turbulent jet impinging normally onto a flat surface. The results cover a wider range of Reynolds number and ratio of impingement height (H) to nozzle gap (D) than do previous studies. The pressure distributions are nearly Gaussian, independent of Reynolds number, and closely balance the momentum flux from the jet nozzle as H/D varies. Particular attention was paid to probe size in measuring the wall shear stress because this has a significant effect on the results. A range of Preston tubes and Stanton probes were tested from which it was found that a 0.05-mm-high Stanton probe—the smallest that we could make—appeared to give accurate results. As expected, the shape of the wall shear stress distributions depended both on H/D and on Reynolds number. Furthermore, the relation between wall pressure and shear stress from Hiemenz's theoretical solution for stagnation flow is not in agreement with the results. It is postulated that the discrepancy is due to the relatively high free-stream turbulence level in the jet. Future papers will document the mean flow field and turbulence and the time dependence of the surface pressure.     

Adsorptive Transfer Stripping for Quick Electrochemical Determination of microRNAs in Total RNA Samples

Electrochemical methods hold promise for fast and inexpensive determination of cancer biomarkers, including microRNAs playing an important role in regulation of gene expression. We developed a simple assay utilizing (i) microRNA labeling with osmium(VI) complexes, (ii) hybridization of microRNA with magnetic bead‐immobilized capture probe, and (iii) adsorptive transfer stripping (AdTS) technique in which working electrode is dipped into a microliter‐sized drop for direct adsorption of microRNA. Increased sensitivity and decreased sample consumption was achieved, and nanogram quantities of microRNA present in 500‐fold excess of total RNA were determined. Our results indicate only negligible interference during hybridization from other RNA molecules.     

Adsorptive Cathodic Stripping Voltammetric Method for Determination of Gallium Using an In Situ Plated Lead Film Electrode

The in situ plated lead film electrode was proposed for the first time for adsorptive stripping voltammetric determination of gallium in water samples. The method was based on simultaneous lead film formation and Ga(III)‐cupferron complex preconcentration at ?0.7 V and its cathodic stripping during the potential scan. The composition of the supporting electrolyte, cupferron concentration, conditions of lead film formation, potential and time of accumulation were studied in detail. Under optimum conditions the limit of detection was 3.8×10^?9 mol L^?1. The proposed procedure was validated in the course of Ga(III) determination in waste water certified reference materials.