Signal enhancement in adsorptive stripping voltammetry of Pt by forced convection during the measurement step

Adsorptive stripping voltammetry (‘formazone-method’) is already known as one of the most sensitive methods for platinum analysis with a detection limit in the low picograms range. In this work, it is shown that the detection limit can be lowered even more by one order of magnitude to 0.2 pg (=1 fmol) Pt in 15 mL electrolyte, corresponding to 68 fmol/L, by applying forced convection during the stripping step of the voltammetric measurement. The sensitivity of the method (given in nA/pg Pt) is enhanced by a factor of 3-5 (in differential pulse mode and 15 mL vial), up to a factor of 30 (using square-wave mode and 3 mL vial). The maximum enhancement factor is limited by the maximum stirrer speed, which can be applied without negative effects on the hanging mercury drop electrode.To check for similar enhancement effects in other types of stripping methods, the behaviour of adsorptive stripping voltammetry for Pt is compared to conventional anodic stripping voltammetry (ASV) of lead, and to adsorptive stripping voltammetry of nickel and cobalt using their dimethylglyoxime (DMG) complexes. No enhancement effect is observed in ASV of lead upon stirring, and the nickel-DMG-system exhibits only a smaller enhancement factor of about 1.5. A reasonable explanation of the higher signal enhancement in the catalytic Pt-formazone-system is the mass transport of reaction products, namely hydrogen, away from the working electrode during the catalytic hydrogen evolution cycle.     

Cancer classification based on microarray gene expression data using a principal component accumulation method

The classification of cancer is a major research topic in bioinformatics. The nature of high dimensionality and small size associated with gene expression data,however,makes the classification quite challenging. Although principal component analysis (PCA) is of particular interest for the high-dimensional data,it may overemphasize some aspects and ignore some other important information contained in the richly complex data,because it displays only the difference in the first twoor three-dimensional PC subsp...     

胰岛素异常积累诱发转移性致癌通路激活的模型化研究

本文基于质量作用动力学与Michaelis-Menten方程建立理论模型,研究胰岛素异常积累诱发转移性致癌通路激活特性.理论模型考虑胰岛素通过激活PI3K-AKT-mTOR信号传导途径调控AKT-MDM2-P53-PTEN信号通路,以及胰岛素异常积累诱发JAK2/STAT5转移性致癌通路信号激活特性.研究发现,在JAK2/STAT5通路信号传导过程中,酪氨酸磷酸化的STAT5单体迅速转化为STAT5二聚体.随着异常胰岛素积累的增加,磷酸化的STAT5二聚体、酪氨酸磷酸化STAT5二聚体表达水平进一步提升.由此表明了,异常胰岛素积累诱发JAK2/STAT5转移性致癌通路激活.胰岛素异常积累通过直接提升JAK2的表达,导致了AKT的表达异常升高,致使细胞糖原代谢紊乱,P53蛋白抑癌作用降低,促进的癌症的发生发展. miR-378作为非常重要的抑癌因子,在JAK2/STAT5转移性致癌信号通路信号作用下,miR-378的抑癌效应被明显削弱,由此也表明了转移性癌症的复杂性.通过分析模型中各参数的敏感性,确定了JAK2/STAT5信号通路创设致癌微环境的灵敏性.本文理论结果符合实验理论观测,可为...     

A3钢损伤累积过程的声发射监测

研究Ａ３结构钢，损伤累积过程中的声发射特性，对其在静、动载荷下声发射参数进行了分析。声发射振铃的上升、下降与材料内部的损伤程度有关。在一定的条件下，可以根据声发射信号的强弱、上升及下降的趋势，判别材料内部的损伤程度．     

High grating efficiency by energy accumulation in a leaky mode

A diffractive slab structure comprising a mirror, a dielectric film, and a grating in the film is made to always exhibit 100% diffraction efficiency for the – 1st order pointing in a backward direction. The design is obtained by sole interference reasoning, and confirmed numerically.     

含酮基吸附剂对莱鲍迪甙A的吸附选择性研究

合成了一系列具有不同骨架结构的中极性含酮基大孔吸附树脂，研究了树脂极性与骨架结构的关系，讨论了树脂对甜菊糖中两种主要糖甙甜菊甙及莱鲍迪甙Ａ的吸附能力和吸附选择性，并设计通过树脂柱的动态色层法从甜菊甙含量高的甜菊糖中成功地分离出高莱鲍迪甙Ａ糖产品．     

Magnetization reversal and spin accumulation in nonmagnetic metals by spin injection from lateral Co/Cu,Co/Al heterojunctions

We have fabricated ferromagnetic/nonmagnetic (FM/NM) metal heterojunctions for the detection of the spin accumulation effect in different nonmagnetic metals. To understand the effect of spin accumulation in more detail, the switching behavior of the ferromagnetic wires was studied by means of magnetoresistance (MR) measurements and Monte Carlo simulations (MC). The polycrystalline heterojunctions were prepared by high-resolution electron beam lithography (HR-EBL) and a special oblique evaporation technique. The ferromagnetic (FM) and the nonmagnetic (NM) metal were evaporated on top of each other in a single-evaporation step to achieve an interface between the two metals of high quality. To verify the quality of the interface, we measured the spin accumulation effect in nonmagnetic copper (Cu) and aluminum (Al) and determined the spin polarization of the current at the interface between the ferromagnetic and nonmagnetic metals.     

Novel,Sensitive Voltammetric Methods for Titanium Determination Using Chromotropic Acid and Azo‐Compounds as Complexing Agents

Voltammetric behavior of titanium(IV) complexes with chromotropic acid, its azo‐derivatives: 2‐(4‐sulfophenylazo)‐1,8‐dihydroxy‐3,6‐naphthalenedisulfonic acid (SPANDS), chromotrope 2B, sulfonazo III and other azo‐compounds: calmagite, tropeoline O and kalces was investigated at a hanging mercury drop electrode. These complexes strongly adsorb onto the electrode, thus can be determined by an adsorptive stripping voltammetry (optimal pH about 6). At pH about 3 reduction current enhancement for Ti‐kalces complex was observed in the presence of chlorate ions. It is a rare example of a catalytic process with azo‐compound as a complexing agent. Signal for Fe‐calmagite complex reduction was also observed. Influence of foreign ions and the optimal conditions for titanium determination are described in detail. Additionally, a connection between obtained results and a structure of titanium complexes is discussed.     

Determination of Aluminum by Adsorptive Cathodic Stripping Voltammetry with 1,2‐Dihydroxyanthraquinone‐3‐Sulfonic Acid (DASA): Effect of Thin Mercury Film Electrode

An analytical technique for aluminum (Al) based upon the complexation reaction between Al and the ligand – DASA (1,2‐dihydroxy‐anthraquinone‐3‐sulfonic acid) has previously been implemented successfully at the hanging mercury drop electrode (HMDE). There are several advantages of using mercury film electrodes (TMFE) over the HMDE, particularly if disposal of mercury is of concern. The novelty of using TMFE for adsorptive cathodic stripping voltammetry (ACSV) of Al – DASA is demonstrated in this paper. The peak potential used for the detection of Al in this system was at ?1.15 V (vs. Ag/AgCl). The method produced a limit of detection (LOD) of 1 μM (n=5) and a linear working range of 1–20 μM Al. Atomic force microscopy methods were used to investigate the nature of the TMFE and its interaction with DASA. The mercury droplets on the TMFE have a limited volume and this may lead to overloading of the electrode at relatively low concentrations of DASA. Interferences from Fe, Ca, Zn and Mg were investigated with only Fe appearing to interfere with the Al‐DASA system. Two masking agents (o‐phenanthroline and 2,2′‐bipyridyl) were shown to be effective at preventing the Fe interference.     

A comparison study of adsorptive transfer voltammetry and solution phase voltammetry for the determination of caffeic acid

This study reports a comparison of adsorptive transfer and solution phase voltammetric methods for the study of caffeic acid. For this purpose, a platform was prepared by the modification of glassy carbon electrodes (GCEs) with MWCNTs and samarium nanoparticles (SmNPs) by means of an ultrasonic bath. The surface morphology of the platform was characterized using SEM, EDX and XRD. The adsorptive transfer voltammetric method was based on the adsorption of caffeic acid (CFA) at the surface of the modified electrode by keeping it into a solution of CFA. Afterwards, the modified electrode was transferred with the adsorbed species in a cell containing only 0.1 mol L⁻¹ phosphate buffer solution (PBS) for the analysis. The current response of CFA was found to be linear over a concentration from 5.0 × 10⁻¹⁰ mol L⁻¹ to 1.0 × 10⁻⁷ mol L⁻¹. The values of the limit of detection (LOD) and limit of quantification (LOQ) were 2.0 × 10⁻¹⁰ mol L⁻¹ and 6.67 × 10⁻¹⁰ mol L⁻¹, respectively. The adsorptive transfer method using the modified electrode (SmNPs/MWCNTs/GCE) has successfully been applied to food samples for determining CFA. The solution phase voltammetry was carried out by dipping the electrode into a voltammetric cell containing CFA. The plot of peak currents was linear over the concentration range of 5.0 × 10⁻⁹ mol L⁻¹ –8.0 × 10⁻⁸ mol L⁻¹. The values of LOD and LOQ were 2.0 × 10⁻⁹ mol L⁻¹ and 6.67 × 10⁻⁹ mol L⁻¹ for CFA using a classical solution phase voltammetry at the proposed platform. It was shown that the LOD obtained at adsorptive transfer voltammetry was 10-fold lower when compared to classical solution phase voltammetry.