微波消解-FAAS测定山药中的5种元素

采用微波消解-火焰原子吸收光谱法测定不同品种山药中常量元素C a,微量元素F e、Cu、M n、Zn的含量。结果表明,山药中被检测的5种元素含量丰富,但品种间差异较大;各元素回收率在94.5%—104.0%之间。该方法简便、快速、结果准确,是山药中微量元素检测的理想方法。     

Direct analysis of fatty acid profile from milk by thermochemolysis-gas chromatography-mass spectrometry

The fatty acid composition of milk is of considerable interest due to their nutritional and functional properties. Although rapid milk fat separation and transesterification procedures have been developed, the overall procedure remains time consuming, specially, for the analysis of a large number of samples. In this work, a fast and simple method for direct profiling of fatty acids from milk using thermochemolysis has been developed. This method has the capability of directly analyse fatty acids from one drop of milk without fat extraction or cleanup. Our approach for thermochemolysis is based on thermal desorption integrated with a cold trap inlet. The optimized method does not present isomerisation/degradation of polyunsaturated fatty acid and shows milk fatty acid profiles comparable to the conventional method based on fat extraction and alkaline transesterification. Overall, this method has demonstrated significant potential for high throughput analysis of fatty acids in milk.     

碱金属助剂类型及前驱物对改性NiAl复合氧化物催化分解N2O活性的影响

制备了不同Ni/Al原子比的NiAl类水滑石样品,焙烧获得NiAl复合氧化物,用于N₂O分解反应,研究了NiAl复合氧化物组成对催化活性的影响。在活性较高的NiAl复合氧化物表面浸渍碱金属碳酸盐溶液,制备改性NiAl复合氧化物,考察了碱金属类型（Na、K、Cs）和钾前驱物（K₂CO₃、K₂C₂O₄、CH₃COOK、KNO₃）对改性催化剂活性的影响。用XRD、ICP-AES、FT-IR、BET、H₂-TPR、XPS技术表征了催化剂的组成结构。结果表明,Ni/Al原子比为2.7的NiAl复合氧化物催化活性较高;Na、K、Cs碳酸盐改性NiAl复合氧化物均提高了催化剂活性,其中K的助剂效应最强。钾前驱物对K改性NiAl复合氧化物的催化活性有显著影响,其中碳酸钾、醋酸钾、草酸钾的加入明显提高了改性催化剂的催化活性,而加入硝酸钾反而降低了催化剂活性。     

基于手持式X荧光光谱仪对乐山大佛赋存砂岩的分析

为探索手持式X荧光光谱仪在石窟研究和保护中的应用,结合岩相分析和前期地调数据,使用手持式X荧光光谱仪,对四川乐山大佛从佛脚到胸部位置共42 m厚的砂岩以平均0.5 m间隔进行高密度XRF测试,做出元素含量和比值变化曲线。研究结果显示,手持式XRF测试结果中的Si,Ca,Al和Fe等主量元素可以较好地与岩相分析结果和自然层划分结果吻合,反映石英、方解石、褐铁矿的含量变化以及岩屑绢云母化程度。元素比值能够反映厚层块状岩体内部的抗风化能力差异,Si/(Si+Fe+Al)可以反映砂岩胶结物含量变化和受溶蚀程度,(K₂O+CaO)/Al₂O₃指示抗化学风化强度变化,S元素含量与Fe、Mn元素的去耦合指示了溶孔发育,综合反映了大佛赋存岩体在胶结物成分、孔隙度和层理发育方面的情况。Cl元素的两段高值与乐山大佛胸部带状滞状区及大佛脚部潜水区高度吻合。手持式X荧光光谱仪应用在石质文物分析中具有以下三个优势：（1）对大型、不可移动的石质文物本体来说,手持式X荧光光谱仪提供了高效、无损的岩石化学成分分析手段,主量元素的含量及分布可以较好地与赋存岩体的岩相分析结果和自然层划分结果吻合,能够成为石质文物本体岩性和岩层划分的辅助手段,有利于进行不同区域石质文物的对比研究。（2）对凿造于同一厚层块状岩层中的石质文物来说,手持式X荧光光谱仪能够满足测试间隔不到0.1 m的高分辨XRF扫描,元素比值的波动和元素间耦合关系的变化反应胶结物成分、孔隙度、溶孔发育度等方面反应块状岩体抗风化能力的内部差异。（3）Cl元素含量变化曲线可以精确指示含水量高的岩层,有助于进行滞水、透水情况和水患防治重点的评估,为处于不同气候和水文条件下的石质文物进行病害位置和机制对比提供辅助信息。     

烟火剂型底排药中氯丁橡胶和松脂酸钙测定方法研究

烟火剂型底排药成分分析用甲苯-乙酸乙酯混合溶剂溶解氯丁橡胶、松脂酸钙和六次甲基四胺,通过蒸馏水萃取除去六次甲基四胺组分,盛装于烧杯中蒸干的氯丁橡胶、松脂酸钙再用乙酸乙酯溶解松脂酸钙转移分离,从而实现氯丁橡胶和松脂酸钙定量分离检测研究。产品检测应用表明,甲苯一乙酸乙酯混合溶剂对单质氯丁橡胶、松脂酸钙、六次甲基四胺回收率在98％以上。试验研究和实际产品检验中,氯丁橡胶、松脂酸钙硷测误差均在±1．5％内（相对误差小于10％）.该方法也可应用于类似混合炸药的成分分析。     

Multiwfn: a multifunctional wavefunction analyzer

Multiwfn is a multifunctional program for wavefunction analysis. Its main functions are: (1) Calculating and visualizing real space function, such as electrostatic potential and electron localization function at point, in a line, in a plane or in a spatial scope. (2) Population analysis. (3) Bond order analysis. (4) Orbital composition analysis. (5) Plot density-of-states and spectrum. (6) Topology analysis for electron density. Some other useful utilities involved in quantum chemistry studies are also provided. The built-in graph module enables the results of wavefunction analysis to be plotted directly or exported to high-quality graphic file. The program interface is very user-friendly and suitable for both research and teaching purpose. The code of Multiwfn is substantially optimized and parallelized. Its efficiency is demonstrated to be significantly higher than related programs with the same functions. Five practical examples involving a wide variety of systems and analysis methods are given to illustrate the usefulness of Multiwfn. The program is free of charge and open-source. Its precompiled file and source codes are available from http://multiwfn.codeplex.com.     

Relating glass formation to eutectic composition in Cu100-xZrx alloy by molecular dynamics simulation

The relationship between eutectic compositions and glass-forming ability (GFA) in Cu_100-xZr_x (x = 8–83) system is studied by molecular dynamic (MD) simulation based on the embedded atom method (EAM). Local maxima of GFA occur in Cu₅₆Zr₄₄, Cu₄₇Zr₅₃ and Cu₃₁Zr₆₉ alloys, close to eutectic points in Cu-Zr binary phase diagram. The structural parameters indicate that the heterogeneous Cu-Zr pairs exhibit stronger and more stable interaction than that of homogeneous pairs. The small peak with a negative amplitude ahead of the main peak in S_CuZr(Q) also implies the preference of Cu-Zr pairs. The avoidance of Cu-Cu neighbours and Zr-Zr neighbours, which correspond to the prepeak prior to the main peak of S_CuCu(Q) and S_ZrZr(Q), leads to structural order on intermediate length scales. Perfect and defect icosahedra constitute medium range order (MRO) clusters by sharing atoms, which promotes the glass formation.     

Role of Acid-Base Equilibria in the Reduction of Selenious(IV) Acid

ABSTRACT

Electroanalytical methods have been widely used for determination of Se(IV), but the nature of the reduction processes involved is not well understood. Polarographic reduction occurs in three waves (i₁, i₂, and i₃) the height of which changes with pH. We proved that in wave i₁, H₃SeO₃ ⁺ is reduced, in i₂ H₂SeO₃, and in i₃ HSeO₃ ^-. SeO₃ ^2? is not reducible. All reductions involve a transfer of six electrons and yield selenides. Limiting currents are controlled by the rate of protonation. As proton donors, in addition to H₃O⁺, the acid forms of the buffer present also act. Limiting currents increase markedly with increasing concentration of the buffer. Tenfold increase in buffer concentration can result in up to 200% increase in limiting current.     

Elemental composition and fatty acid profile of the edible fruits of Amatungula (Carissa macrocarpa) and impact of soil quality on chemical characteristics

The Amatungula fruit, from Carissa macrocarpa, is commonly consumed by the local people of KwaZulu-Natal (KZN), South Africa. Levels of elements in the fruit were determined to assess if they conform to recommended dietary allowances (RDAs) and to assess for potential toxicities. Soils and fruit samples from nine sites in eastern KZN were investigated. Concentrations of elements in the fruit were found to be in the order of Ca > Mg > Fe > Mn ≈ Cu ≈ Pb > Se > Cr > Ni > Zn. For the elements in focus, except for Pb, all of the elements found in the fruit contribute significantly towards the RDAs. Lipid profiling was also done to determine the fruits potential as a source of essential fatty acids. The fruit was rich in monounsaturated and essential fatty acids with the linoleic acid to α-linolenic acid ratio conforming to the recommended range for cardiac health. Concentrations of elements in soil had no significant effect on plant concentrations, but competition between elements in soil influenced their availability. Total soil concentrations of most metals studied have significantly correlated Pb availability, indicating the impact of these metals on Pb availability. The Amatungula fruit showed tendency to accumulate Pb, with Pb levels in fruit at all sites being toxic to human health. Site location had a major effect on plant concentrations however uptake and distribution was primarily dependent on the plants inherent controls, as evidenced by the accumulation and exclusion of elements, to meet its physiological requirements.     

Determination of the Mineral Composition of Watercress and Data Evaluation Using Multivariate Analysis

This paper reports the determination of the mineral composition of watercress (Nasturtium officinale Cruciferae, Brassicaceae), grown in soils from three cities in the Bahia State of Brazil, and in a fourth city where plants were grown in a hydroponic system. The sampling was carried out during the summer and winter. Analyses were performed with inductively coupled plasma optical emission spectrometry (ICP OES), and the accuracy was confirmed with a certified reference material of apple leaves.

Principal component analysis (PCA) and hierarchical cluster analysis (HCA) revealed different mineral compositions of the samples collected in the summer and winter.

Samples collected in the summer had a higher concentration of the nutrients iron, calcium, and magnesium, and the samples collected in the winter had a higher concentration of manganese and copper. The average contents of the samples (expressed as wet weight) were 2.50 and 3.03 mg g^?1 for calcium, 0.37 and 0.86 mg g^?1 for magnesium, 8.68 and 10.84 µg g^?1 for iron, 8.42 and 8.47 µg g^?1 for zinc, 0.61 and 0.47 µg g^?1 for copper, and 7.78 and 5.03 µg g^?1 for manganese for summer and winter, respectively. These results are in agreement with values previously reported in the literature. Samples collected from the hydroponic system in the winter had a lower concentration of all nutrients.