LaNi_5和LaNi_(4 .7)Al_(0 .3)氢化物柱内氢氘间的排代

进行了室温附近LaNi5和LaNi4 .7Al0 .3 两种材料上气 固间氢氘的排代实验。两种材料的排代效果都较好 ,相比之下 ,LaNi5的更优。可以推测 ,在不要求得到高纯氚的情况下 ,都可以用作氚的冷卸载贮存床。初步的理论探讨揭示 ,气 固界面的化学交换反应是产生排代效应的原因 ,宏观交换规律决定排代效果。理想化的塔板理论模型对排代流出曲线的描述是有效和适用的 ,塔板高度是材料排代性能优劣的指标 ,在确定的排代条件下 ,如果塔板高度小于 1.0cm ,应该认为具有较好的排代效果。     

氢化物发生-原子荧光光谱法(HG-AFS)测定特硬铅合金中硒和碲

建立了氢化物发生-原子荧光光谱法(HG-AFS)测定特硬铅合金中硒和碲的分析方法。试样经硝酸和酒石酸溶解,硫酸沉淀分离基体铅元素。移取部分试液,在40%盐酸介质中直接用氢化物发生-原子荧光光谱法(HG-AFS)测定样品中的硒;另移取部分试液,加入氢溴酸挥发除去砷、锑、锡、硒等元素,在40%盐酸介质中用氢化物发生-原子荧光光谱法(HG-AFS)测定样品中的碲。考察了测定的最佳条件、铅及共存元素对测定的影响。测定硒和碲的相对标准偏差分别为7.5%～9.3%和3.6%～13.0%,加标回收率分别为88%～92%和98%～102%。准确度和精密度均能满足分析需要,具有较强的实用性。     

氢化物发生-原子吸收光谱法测定食品中的汞

研究了采用氢化物发生-原子吸收光谱法测定食品中痕量汞的方法,通过采用氢化物发生器,选择合适浓度的载流和硼氢化钾,获得了较为满意的分析结果。在测定汞含量5～20μg/kg的食品标准样品时,测试结果相对标准偏差RSD为2.2%～3.7%,回收率为84.9%～97.5%,检出限为0.2μg/L,完全满足食品行业汞元素痕量检测要求,操作简便、快速。     

Demethylation of trimethylantimony species in aqueous solution during analysis by hydride generation/gas chromatography with AAS and ICP MS detection

The method of hydride generation for the speciation of antimony compounds was examined with respect to the problem of molecular "rearrangement'. Specifically, demethylation of trimethylstilbine during the analysis of trimethylantimony dichloride (Me₃SbCl₂) was studied. Previously published observations that enhanced demethylation takes place as a result of inadequate preconditioning of the analytical apparatus were found to be not reproducible. However, demethylation was enhanced as the pH decreased when using two different analytical methods: semi-continuous flow hydride generation–gas chromatography–atomic absorption spectrometry (HG– GC–AAS), and batch-type hydride generation– gas chromatography–inductively coupled plasma mass spectrometry (HG–GC–ICP MS). Applications of the hydride generation method to environmental samples revealed differences in analytical results at high and low pH, and enhanced demethylation taking place because of the matrix in a fungal extract sample. The authors recommend that researchers using the method of hydride generation for antimony compounds carefully test the reaction conditions with standard compounds and use the method of standard addition only. © 1998 John Wiley & Sons, Ltd.     

MLi2H3(M=Na,K)与NH3反应的密度泛函理论研究

采用杂化密度泛函方法,对MLi₂H₃(M=Na, K)团簇与NH₃的反应机理进行计算分析,对反应中各驻点几何构型进行优化,经频率分析和内禀反应坐标计算以确证各驻点的正确性和连接关系.经单点能校正计算,给出反应相关的能量信息.结果表明：引入Na和K原子后,反应物LOMO轨道有大幅度的向Na、K原子处的转移. KLi₂H₃有较小的能隙和电离势及较高的费米能,有较高反应活性. Na、K元素的引入,能破坏反应物的稳定性,降低反应能垒.     

Evidence supporting the presence of dissolved dimethylarsinate in the marine environment

Experiments have been carried out to test the commonly held belief that the dissolved dimethylarsenic species present in marine waters is dimethylarsinate. By employing a novel combination of HPLC and cryogenic‐trap hydride generation atomic absorption spectroscopy (HG AA), the sensitivity limitations of conventional in‐line HPLC instrumentation can be overcome, permitting dimethylarsinate to be measured by HPLC at levels below 200 pg cm⁻³. A comparison of results obtained by this procedure with those obtained by direct cryogenic‐trap HG AA demonstrated that much of the dissolved dimethylarsenic present in the mouth of the Beaulieu River estuary (Hampshire, UK) had HPLC retention characteristics consistent with the presence of dimethylarsinate. Copyright © 1999 John Wiley & Sons, Ltd.     

Crystal,electronic structure and hydrogenation properties of the Mg5.57Ni16Ge7.43 cluster phase with a new type of polyhedron

The ternary germanide Mg_5.57Ni₁₆Ge_7.43 (cubic, space group Fmm, cF116) belongs to the structural family based on the Th₆Mn₂₃-type. The Ge1 and Ge2 atoms fully occupy the 4a (mm symmetry) and 24d (m.mm) sites, respectively. The Ni1 and Ni2 atoms both fully occupy two 32f sites (.3m symmetry). The Mg/Ge statistical mixture occupies the 24e site with 4m.m symmetry. The structure of the title compound contains a three-core-shell cluster. At (0,0,0), there is a Ge1 atom which is surrounded by eight Ni atoms at the vertices of a cube and consequently six Mg atoms at the vertices of an octahedron. These surrounded eight Ni and six Mg atoms form a [Ge1Ni₈(Mg/Ge)₆] rhombic dodecahedron with a coordination number of 14. The [GeNi₈(Mg/Ge)₆] rhombic dodecahedron is encapsulated within the [Ni₂₄] rhombicuboctahedron, which is again encapsulated within an [Ni₃₂(Mg/Ge)₂₄] pentacontatetrahedron; thus, the three-core-shell cluster [GeNi₈(Mg/Ge)₆@Ni₂₄@Ni₃₂(Mg/Ge)₂₄] results. The pentacontatetrahedron is a new representative of Pavlyuk's polyhedra group based on pentagonal, tetragonal and trigonal faces. The dominance of the metallic type of bonding between atoms in the Mg_5.57Ni₁₆Ge_7.43 structure is confirmed by the results of the electronic structure calculations. The hydrogen sorption capacity of this intermetallic at 570 K reaches 0.70 wt% H₂.     

离子色谱-双阳极电化学氢化物发生-原子荧光光谱法测定Ⅰ型牙髓失活材料中的砷形态

将自制的双阳极电化学氢化物发生器作为离子色谱与原子荧光光谱的联用接口,建立了离子色谱-双阳极电化学氢化物发生-原子荧光光谱法在线分析砷形态系统.最佳实验条件为淋洗液6.0 mmol/L NH4H2PO4(pH 6.20),电解液0.40 mol/L H2SO4,电解液流量为阳极4.0 mL/min,阴极 1.5 mL/min,电解电流密度0.50 A/cm.2,载气流量300 mL/min,屏蔽气流量500 mL/min,氢气流量80 mL/min.在优化的实验条件下,As(Ⅲ)、DMA、MMA的线性范围为5～200 μg/L、As(Ⅴ)的线性范围为10～200 μg/L,As(Ⅲ)、DMA、MMA和As(Ⅴ)检出限分别为3.04、4.27、3.97和9.30 μg/L(信噪比S/N=3).50 μg/L的As(Ⅲ)、DMA、MMA和As(Ⅴ)混合标准溶液平行进样7次,得到的色谱峰面积的相对标准偏差(RSD)分别为415%、3.08%、519%和3.62%.将该方法用于牙髓失活材料中的砷形态分析.     

Direct determination of arsine in gases by inductively coupled plasma-dynamic reaction cell-mass spectrometry

Reliable determination of arsine (AsH₃) in gases is of great importance due to stringent regulations associated with health, safety and environmental issues. It is, however, challenging for an analyst to determine trace airborne arsine concentrations without specifically designed collection procedures using adsorption, desorption, dissolution or impinging techniques. To circumvent such technical barrier, we have newly developed a direct analytical method, characterized by introduction of an arsine gas sample into stable plasma stream, followed by gas-phase oxidation of arsine with molecular oxygen in a dynamic reaction cell (DRC) equipped within the inductively coupled plasma-mass spectrometry (ICP/MS) system, followed by subsequent detection of AsO⁺ ion. This preliminary work used trace arsine concentrations (161 μg m⁻³, 322 μg m⁻³, and 645 μg m⁻³) gravimetrically prepared in N₂ balance. The proposed method was optimized for the important experimental parameters such as the flow rates of the reaction gas, the arsine sample, and the carrier gas. This method was then validated by demonstrating good figure-of-merits including the low limit of detection (0.10 μg m⁻³), good linearity (r² > 0.9915), low measurement uncertainty (0.66%), and high speed of analysis (<6 min). The proposed method is expected to be potentially applicable to the determination of arsine in real workplace air after appropriate modifications are made.     

Kinetics of Hydride Abstractions from 2‐Arylbenzimidazolines

The rates of the hydride abstractions from the 2‐aryl‐1,3‐dimethyl‐benzimidazolines 1a – f by the benzhydrylium tetrafluoroborates 3a – e were determined photometrically by the stopped‐flow method in acetonitrile at 20 °C. The reactions follow second‐order kinetics, and the corresponding rate constants k₂ obey the linear free energy relationship log k₂(20 °C)= s(N+E), from which the nucleophile‐specific parameters N and s of the 2‐arylbenzimidazolines 1a – c have been derived. With nucleophilicity parameters N around 10, they are among the most reactive neutral C? H hydride donors which have so far been parameterized. The poor correlation between the rates of the hydride transfer reactions and the corresponding hydricities (ΔH⁰) indicates variable intrinsic barriers.