氢化物负压发生器—真空无火焰原子化器的原子吸收光谱法测定碲

在负压发生器中用1％NaBH_4将Te(Ⅳ)还原成碲化氢后,再加入2mL氧气,用真空泵将氧与碲化氢的混合物吸进电热真空石英管中,同时测定原子吸收光谱。加入的氧与硼氢化钠分解产生的氢反应生成水分子,消除了氢对碲的干扰。     

硒、碲氢化物发生的反应机理和反应条件

元素周期表中ⅣA,ⅤA及ⅥA族元素的化学及物理性质的周期性变化引起硒、碲两元素的氢化物生成反应机理的改变。文中对两元素生成氢化物的反应机理作了解释,认为是硒(Ⅳ)[或碲(Ⅳ)]在盐酸溶液中与初生态氢[H]反应的结果。初生态氢是由硼氢根(BH4-)在酸溶液中水解而产生,反应时随氢离子(即酸度)浓度的增加,氢化物的生成率将明显提高。此外,不断地将氢化物发生反应中同时生成的水蒸气除去不仅可避免硒(碲)氢化物被氧化,而且还可提高其产出率和峰值测定的重现性。对如何规范使用低熔点、高强度空心双阴极灯也作了评价。     

氢化物负压发生和真空无火焰原子化器的原子吸收光谱法测定铋

在负压发生器中用1% NaBH_4将Bi(Ⅲ)还原为铋化氢后,向发生器中加入一定量的空气。用真空泵将铋化氢和空气的混合物同时吸入到真空电热石英管中,用原子吸收仪器测定。在原子化器内,加入空气中的氧与硼氢化钠分解产生的氢反应,生成水分子。因而消除了氢对测定铋的干扰。     

氧、氮、氢分析仪校准方法探讨

建立了氧、氮、氢分析仪的校准方法,介绍了氧、氮、氢分析仪的工作原理、校准要求、校准用标准物质.以北京纳克分析仪器有限公司生产的ON-3000氧氮分析仪和H-3000氢分析仪作为校准对象,对校准方法进行了验证.该方法已作为评价氧、氮、氢分析仪的依据并得到认可.     

水中微量砷、硒的原子吸收分光光度测定

利用氩氢火焰-氢化物还原技术的原子吸收分析方法是一较好的砷、硒测定方法。我们用硼氢化钾作为还原剂,将砷(硒)还原为氢化物,贮于一小橡皮球内,然后送入氩氢火焰对水中砷(硒)进行了测定,得到满意的效果。灵敏度(1％的吸收)砷为0.016微克,硒为0.02微克。 1.仪器:所有测定在Perkin-Elmer 403型原子吸收分光光度计上进行。用056型记录器记录峰值。应用三缝燃烧器。氘灯背景校正。砷、硒空心阴极灯。砷、硒分析装置如图1:     

钛-钒合金及其氢化物的第一原理研究

用局域密度泛函近似 ( L DA)与赝势方法研究了钛钒合金氢化物的结构与组成的关系。结果表明 ,V的含量小于 30 % ,Ti- V合金将不能稳定在 bcc向 bct转化 ,含 Ti量高于 70 %的 Ti- V合金氢化物不能稳定在 bcc相。所计算的各种 Ti- V氢化物的体胀率小于 2 .5% ,比相同含 H量的纯 V氢化物的体胀率小 ,Ti- V合金有利于抗氢脆 ,但不利于对氢的贮存。     

过渡金属多氢化物催化的选择性转移氢化

研究过渡金属多氢化物和分子氢络合物(非经典过渡金属多氢化物)催化下,以异丙醇为氢源,还原环酮和非环酮为相应醇的立体选择性的变化,并研究不同膦配体对4-甲基环已酮还原的立体选择性影响。探论了在温和条件下以Ru分子氧络合物为催化剂,外加手性配体情况下,对苯已酮氢化反应的对映选择性的影响。     

氢化物-氧屏蔽空气乙炔火焰原子吸收法测定锗分析条件的研究

在原子吸收分析中,由于利用氢化物生成反应,大大提高了砷、锑、铋、碲、锡、铅、锗以及硒八个元素的测定灵敏度,国外使用氩氢焰和一氧化二氮-乙炔焰,进行锗的氢化物原子吸收法测定。在此基础上,我们采用磷酸钠为增感剂,结合氧屏蔽原子化方式对锗作了测定。实验部分 1.仪器:WFX-1A型原子吸收分光光度计;AHG-1型半自动氢化物装置。 2.试剂;锗(Ⅳ)标准溶液,10微克/毫升。硼氢化钾溶液5％(含氢氧化钾1.5％),用玻璃过滤漏斗抽滤。磷酸钠20％水溶液。     

锆氢化反应研究 VI:环氧化合物的选择还原

环氧化合物还原成醇,是较为常见的反应。其区域选择性取决于所使用的还原剂。一般规律是:LiAlH_4类型的亲核性复合金属氢化物从空间障碍较小的部位接近氧,从而获得取代基较多的醇;而硼烷(尤其在BF_3存在之下)或铝烷类型的亲电性金属氢化物则使环氧化合物从相反方向开环并主要获得取代基较小的醇。锆氢试剂(Cp_2ZrHCl)对羰基化合物的还原已经详细研究,本文将研究环氧化合物的还原及其区域选择性,并进一步认识锆氢试剂在反应中的作用及其本质。     

稀土在镁合金溶液中作用的热力学分析

本文对多种稀土元素在镁合金溶液中的作用进行了热力学分析，并讨论了稀土在溶液中的去氧和除氢机制，计算结果表明，稀土与镁溶液中的氧化物夹杂发生交互作用，产生稀土氧化物而除去氧化物夹杂，通过与溶液中的氢发生交互作用，产生稀土氢化物而达到了溶液除氢；但与主要成分为ＭｇＣｌ２的熔剂发生交互作用则降低了溶液中的稀土含量。     

氢化物原子吸收机理的研究 Ⅰ.H_2和空气在氢化物原子化中的作用

研究了氢气和空气在氢化物原子化过程中的作用,观察到H_2的存在下不仅引发自由基过程,而且抑制氢化物的热分解.空气的存在,使一些元素氢化物的最佳原子化温度降低,其增感作用只有在H_2共存时才表现出来.在没有H_2共存时,空气可能与氢化物反应生成氧化物,对吸收信号产生抑制.     

Inter-element interferences in the determination of arsenic and antimony by hydride generation atomic absorption spectrometry with a quartz tube atomizer

The interferences between arsenic and antimony on each other during the hydride generation atomic absorption spectrometry (HGAAS) determination of arsenic and antimony using a quartz tube atomizer (QTA) were examined. In order to eliminate or reduce such interferences by selective heat decomposition of arsine and stibine, a Pyrex adsorption U-tube trap containing glass wool was placed between the drying tube and the quartz tube atomizer. Although at 250 °C stibine decomposes and is held almost completely by the trap, arsine is also decomposed to an extent of 24% and, therefore, thermal decomposition is not useful to eliminate antimony interference on arsenic determination. The effect of coating the glass wool in the U-tube with antimony on the arsenic suppression of the antimony signal was studied. The results showed that the antimony coating in the U-tube could not hold arsenic effectively and its interference on the antimony signal could not be eliminated by this means. In the second part of the study, oxygen was supplied to the quartz tube atomizer during atomization in order to study the effect of supplying oxygen on the antimony signal and on the interference of arsenic in the antimony determination. Sensitivity was increased in the presence of oxygen and interferences of arsenic on antimony determination was decreased by about 10% when oxygen was supplied. It was also observed that the extent of interferences depended mainly on the interferent concentration rather than the analyte concentration.     

Determination of antimony, arsenic, bismuth, selenium, tellurium and tin by low pressure atomic absorption spectrometry with a quartz tube furnace atomizer and hydride generation with air addition

A new method has been developed for the determination of antimony, arsenic, bismuth, selenium, tellurium and tin by hydride generation-atomic absorption spectrometry in an electrically heated quartz tube furnace under sub-atmospheric pressure. The hydride generator, operating at a pressure lower than atmospheric, is used to generate and collect the hydrides of these elements. A certain volume (at atmospheric pressure) of air is then added to the generator after the formation of the volatile hydride. The gaseous mixture of the hydride and air is drawn into an evacuated, heated quartz tube by a vacuum pump. The proposed method gives improved sensitivities and detection limits.     

Mechanism of volatile hydride formation and their atomization in hydride generation atomic absorption spectrometry.

The mechanism of volatile hydride generation (HG) and the formation of analyte atoms in the quartz cell atomizer used in the determination of hydride-forming elements (As, Bi, Ge, Pb, Sb, Sn, Te etc.) by atomic absorption spectrometry (AAS), have been critically reviewed. The nascent hydrogen mechanism failed to explain hydride generation under different experimental conditions when tetrahydroborate (THB), amineboreanes (AB) and cyanotrihydroborate (CBH) were used as reductants. Various experimental evidence suggested a non-nascent hydrogen mechanism, in which the transfer of hydrogen directly bonded to boron to an analyte takes place. In electrochemical hydride generation (EcHG), the reduction of the analyte species and subsequent hydrogenation was proposed. The mechanism of analyte atom formation in a quartz tube atomizer has been explained by the following hypotheses: thermal decomposition, oxidation by 02 and collisions by hydrogen free radicals. The free-radical mechanism satisfactorily explains most of the analytical implications. The significant variation in the experimental conditions required to generate different analyte hydrides makes it difficult to arrive at a generalized mechanism of hydride formation.     

Electrochemical Hydride Generation:A Novel Sample Introduction Method for the Non-dispersive Atomic Fluorescence Spectrometry

Production of volatile covalent hydrides of environmentally important elements (As、Se、Bi、Ge、Sn、Sb and Pb) by reaction with sodium (potassium) tetrahydroborate (NaBH₄) in acidic media for determination by atomic absorption has been widely used in routine analysis. However, this technique has several disadvantages. NaBH₄ is a potential source of contamination, its aqueous solution is unstable. As an alternative to chemical hydride generation, hydride generation by electrochemical reduction (EcHG) has been reported in recent years by many authors^[1-3]. Compared with NaBH₄ hydride generation system, the EcHG with subsequent detection by atomic absorption spectrometry offers the high sensitivity, low detection limits, and the absence of interference from the transition metals. However, the hydrogen produced by EcHG reduced greatly, this led to the interference caused by hydride forming elements was serious due to the lack of free hydrogen (H·) radical in the quartz tube during the atomization. EcHG coupled with atomic fluorescence spectrometry system uses Ar-H2 mini-flame as an atomizer, in which the gaseous phase interference can be expected eliminated. In addition, non-dispersive atomic fluorescence spectrometry (NDAFS) system with a quite single structure, is a very sensitive and feasible method for the measurement of elements that form volatile hydrides. By combining with electrochemical hydride generation as a sample introduction technique, it is possible to develop a potential interface for chromatography or capillary electrophoresis in speciation analysis.     

Evaluation of oxidant media for the determination of lead in food slurries by hydride generation atomic absorption spectrometry

Several oxidant media were evaluated for the generation of lead hydride from slurry samples and their application to the determination of lead in vegetables and fish by hydride generation atomic absorption spectrometry. Three oxidant - acid media were compared: hydrogen peroxide - nitric acid, ammonium persulphate - nitric acid and potassium dichromate - lactic acid. The powdered samples were suspended in Triton X-100 and shaken with 10.0 g of blown zirconia spheres until a slurry was formed. The potassium dichromate - lactic acid medium was the most satisfactory for the determination of lead in fish and vegetables, providing the lowest detection limits as a result of its high sensitivity and low blank values. The ammonium persulphate - nitric acid medium gave good accuracy, precision and selectivity for vegetables (1-2 p.p.m. of lead); however, with fish (0.1-1 p.p.m. of lead) it was only a semi-quantitative medium for the determination of lead owing to its lack of sensitivity and selectivity. The hydrogen peroxide - nitric acid medium was unsatisfactory for the generation of lead hydride from slurry samples because of decomposition of hydrogen peroxide by the organic matter in the sample.     

Study of processes in the hydride generation atomic absorption spectrometry of antimony,arsenic and selenium

Studies of the decomposition rate of the reducing agent sodium tetrahydroborate in alkaline and acidic media and of the reaction rate of the formation of the hydrides under the usual analytical conditions are described. The stripping of the hydrides with different lengths of the stripping coil, with different amounts of hydrogen in the carrier gas and with sodium hydroxide added during and after the stripping process are discussed. Some evidence for the existence of an intermediate during the decomposition reaction of the sodium tetrahydroborate is given. The role of temperature, hydrogen and oxygen during the atomization of the hydrides in an electrically heated quartz cuvette is discussed. Under certain conditions, antimony atoms form dimers or elemental antimony precipitates in the heated cuvette.     

Mechanism of atomization interference by oxygen at trace level in miniature flame hydride atomizers

The mechanism of atomization interference by oxygen at trace level in gases supplied to miniature argon hydrogen diffusion flame (MDF), flame-in-gas-shield (FIGS) and flame-in-flame (FIF) hydride atomizers, was investigated for hydrogen selenide, arsine and stibine. A continuous flow hydride generation system coupled with atomic absorption detection was employed. The effect produced by oxygen contamination, intentionally added to gases as contaminant (0–1290 μl l^− 1), on spatial distribution of free atoms, on sensitivity and signal shape observed for MDF, FIGS and FIF in different atomization conditions and on the shape of calibration graphs was investigated. The oxygen contaminant reacts with hydrogen radicals reducing their concentration and the size of hydrogen radical cloud. Simultaneously, the rate of free analyte atom reactions is enhanced. Both these factors lead to the decrease of free analyte atom population.     

Hydride generation – in-atomizer collection of Pb in a quartz trap-and-atomizer device for atomic absorption spectrometry – an interference study

Interferences of selected hydride forming elements (As, Sb, Bi, Se and Sn) on lead determination by hydride generation atomic absorption spectrometry were extensively studied in both on-line atomization and preconcentration (collection) modes. The commonly used on-line atomization mode was found free of significant interferences, whereas strong interference from Bi was observed when employing the preconcentration mode with plumbane collection in a quartz trap-and-atomizer device. Interference of Bi seems to take place in the preconcentration step. Interference of Bi in the collection mode cannot be reduced by increased hydrogen radical amount in the trap and/or the atomizer.