Metallic Impurities within Residual Catalyst Metallic Nanoparticles Are in Some Cases Responsible for “Electrocatalytic” Effect of Carbon Nanotubes

It′s what′s on the inside that counts : In some cases, the metallic impurities within residual catalyst metallic nanoparticle impurities, which remain in carbon nanotubes even after their purification, are responsible for the “electrocatalytic” properties of carbon nanotubes. This is demonstrated by using double‐walled carbon nanotubes (DWCNTs) containing cobalt residual catalyst nanoparticle impurities, which themselves contain iron‐based impurities.

     

Local density of states around two nonmagnetic impurities in cuprate superconductors

The local density of states (LDOS) around two nonmagnetic impurities which are located at different sites is studied within the two-dimensional t-J-U model. The order parameters are determined in a self-consistent way with the Gutzwiller projected mean-field approximation and the Bogoliubov-de Gennes theory. When the two impurities are located one or two sites away, we find the superconductivity coherence peaks are more strongly suppressed and the zero-energy peak (ZEP) has split into two peaks. Whereas when the two impurities are located next to each other, the ZEP vanished, and LDOS does not change a lot compared with the case away from the impurities.     

磁场和量子点尺寸对方形杂质量子点中电子性质的影响

利用二维有限差分方法,计算了含有H_2~+杂质的方形量子点的基态能和杂质束缚能。讨论了磁场和杂质位置对不同尺寸的量子点中电子基态能量和束缚能的影响,得出了方形量子点系统的量子尺寸效应。     

Investigation of influential factors on the purification of zone‐refined germanium ingot

Zone refining is one of the most important procedures to purify germanium crystals for the fabrication of detectors in our laboratory. In order to properly zone refine high‐purity germanium crystals, it is important to develop perfect cleaning procedures for raw materials, quartz tubes, and the containers holding raw materials. Additionally, vacuum levels, container types, the correct combination of ambient gases, the speed of zone travel, and the ratio of ingot length to molten zone length, all need to be carefully studied in order to obtain the best results possible. In this work, we investigate a number of influential factors in perfecting high‐purity germanium crystal growth, specifically: cleaning procedures, boat composition, vacuum levels in the chamber, zone travel speed, and the ratio of ingot length to molten zone length. Using the van der Pauw Hall technique, we were able to measure the electrical properties of zone‐refined ingots and analyze the origin and distribution of three main impurity elements (boron, aluminum and phosphorus) thereby allowing us to study potential contamination sources. After detailed analysis on the various influential factors, we were able to optimize the zone‐refining procedures.     

标准加入ICP-AES法测定铬酸钠中杂质元素

采用ICP-AES法同时测定工业铬酸钠溶液中微量Al,Ca,Fe,Mg,Si杂质元素。针对测定过程中存在的基体干扰、谱线干扰等问题,通过实验确定了铬酸钠中微量的Al,Ca,Fe,Mg,Si的分析测试谱线:Al 167.079nm,Ca 393.366nm,Fe 259.940nm,Mg 279.533nm,Si 251.61nm。实验用优级纯HCl将待测溶液调为酸性,消除工业铬酸钠溶液酸度不稳定引起的测定误差,采用标准加入法消除基体干扰,探讨了Al,Ca,Fe,Mg,Si等五种微量组分检测方法标准曲线线性相关性、检出限、精密度以及回收率等分析指标,详细研究了在选定分析谱线下,标准加入法对铬酸钠溶液中Al,Ca,Fe,Mg,Si等微量杂质含量测定结果的准确性的影响。结果表明标准曲线呈线性关系(R2=0.998 8~0.999 6之间),五种元素检出限在(0.013 4~0.028 0)mg·L-1之间,11次测量标准偏差小于5.86%,回收率在97.30%~107.50%之间。实验建立的分析方法的检出限、精密度、准确度均能满足分析测试要求;方法实用性强,已经成功用于离子膜电解法中铬酸钠原料液微量离子检测;利用铬酸钠、重铬酸钠和重铬酸酐与溶液酸度的关系,实验建立的分析方法还可拓展于重铬酸钠及铬酐甚至其他六价铬产品中Al,Ca,Fe,Mg,Si杂质离子的检测,同时也可以扩展到上述样品中其他杂质元素的测定。     

Nanographite impurities in carbon nanotubes: their influence on the oxidation of insulin, nitric oxide, and extracellular thiols

There has been growing interest in the use of modified-carbon-nanotube electrodes in applications such as the electrochemical detection of biologically significant compounds, owing to their apparent "electrocatalytic" properties and ability to enhance oxidative signals. In spite of their salient properties, little work has been done to further examine the reasons for these reported characteristics. In this report, we present clear evidence that the presence of nanographite impurities within carbon nanotubes (CNTs) is responsible for providing the previously reported enhanced electrochemical response. We have demonstrated this effect on homocysteine, N-acetyl-L-cysteine, nitric oxide, and insulin, which are important biological agents in the body. Moreover, we also showed that the influence of nanographite impurities on the electrochemistry of carbon nanotubes is prevalent among a variety of CNTs, such as single-walled CNTs, double-walled CNTs, and few-walled CNTs. Our findings will have a profound influence upon the biomedical applications of CNTs.     

A New Carrier for Direct Spectrographic Determination of Trace Alkalies and Alkaline Earths in High Purity Thorium Oxide

Abstract

A d.c. arc emission spectrographic method is described for the determination of sub ppm levels of Ba, Li and Sr and ppm levels of Cs, K and Na in high purity thorium oxide. The method which employs RbCl as carrier is simple and rapid and does not involve the use of any special atmosphere for exciting the sample. It was observed that RbCl shows definite improvement over AgCl in carrier action. The carrier distillation technique reported makes possible the following range of estimations: Li: 0.02 – 5.0 ppm, Ba, Sr: 0.5 – 20 ppm, Cs: 2–50 ppm, K,Na: 5–100 ppm. The detection limit obtained by this method for Li and Sr is lower than that obtained by the earlier carrier-distillation methods reported as well as other direct sensitive techniques of Zeidel and Avni for the analysis of Tho₂. The precision of the method ranges from 8% for Cs to 17% for Ba. Volatilization studies on the choice of carrier material are presented.     

The GAS-Chromatographic Determination of Volatile Impurities in γ -Aminobutyric Acid Derivatives

Abstract

The rapid gas-chromatographic analysis of the volatile impurities content in the synthetic preparations of the γ -aminobutyric acid and its derivatives was developed.     

Electrochemical Quantification of Mercury in Solutions Using Boron-doped Diamond Electrodes: Electrode Regeneration and Role of Gold and Impurities

Abstract

For determining Hg in solutions in the ppb to ppt range using boron-doped diamond (BDD) electrochemistry, the role of an added gold solution for enhanced sensitivity is investigated. Using differential pulse anodic stripping voltammetry (DPASV), peaks due to Cu and Ag as impurities from gold are identified. With the proper choice of the potential for deposition, effects of the impurities are minimized and an electrode regeneration procedure is devised and tested, resulting in reproducible slopes of the calibration curves in successive runs. The location and shift of the DPASV peak potentials with concentration are explained with the use of the Nernst equation.     

A Chemometrical Approach to Optimization and Validation of an HPLC Assay for Rizatriptan and its Impurities in Tablets

Abstract

An isocratic reversed‐phase high‐performance liquid chromatographic method was developed and validated for the analysis of a novel antimigraine drug, rizatriptan benzoate, in a dosage form along with its two impurities, L‐749.019 and L‐783.540. The method used a C₁₈ XTerra? (150×3.9 mm), 5 µm column. The mobile phase consisted of a mixture of methanol, TEA (1%) and 10 mM KH₂PO₄ (5:9.5:85.5 v/v) at a flow rate of 1.2 ml min^?1 (pH of the water phase was adjusted to 5.5 with 85% orthophosphoric acid). Column temperature was 20°C and the detection was performed at 225 nm. The central composite design technique and the response surface method were used in the robustness test considerations. The method was applied satisfactorily to the analysis of commercial rizatriptan formulation.