Photo-induced chemical-vapor generation for sample introduction in atomic spectrometry

Chemical-vapor generation (CVG) is widely used as a sample-introduction technique for atomic spectrometry, with the advantages of efficient matrix separation, high analyte-transport efficiency, and high selectivity and sensitivity. Recently, photo-induced CVG (photo-CVG) was demonstrated to be a powerful alternative to conventional CVG. In photo-CVG, volatile species (including hydrides, elemental, carbonylated and alkylated analytes) are generated from non-volatile precursors by ultraviolet irradiation in the presence of low-molecular-weight organic compounds. Photo-CVG is simple, fast and environmentally friendly with little interference from transition metals. Its analytical applications have been demonstrated in analysis of Hg, conventional hydride-forming elements (As, Bi, Sb, Se, Te), transition metals (Ni, Co, Fe) and non-metals (I). In addition, photo-CVG was developed as a simple, effective interface between high-performance liquid chromatography (HPLC) and atomic spectrometry. This review summarizes the applications of photo-CVG for various analytes and as a novel interface between HPLC and atomic spectrometry. We also discuss current research on the possible reaction mechanism of photo-CVG.     

Study of interferences by transition metal ions in hydride generation atomic absorption spectrometry of antimony

The mechanism of the interference of metal ions in the hydride generation atomic absorption spectrometry (AAS) of antimony was studied. Experiments on the decomposition rate of sodium tetrahydroborate in acidic media were done in the presence of interfering metals, with and without the addition of masking agents. The results were compared with experiments on the sensitivity of AAS in the presence of the same interfering metals with and without the addition of the same masking agents. AAS experiments are described in which the product of the reaction between sodium tetrahydroborate and one of the interfering metals was present during hydride formation. This reaction product was certainly one of the causes of interference, but the contribution of the catalytic decomposition of sodium tetrahydroborate to interference is not clear.     

Determination of Antimony in Brass by On-line Hydride Generation Atomic Fluorescence Spectrometry Alkaline Solution

The hydride generation(HG) technique combined with atomic spectrometry as a detection system has become one of the most powerful analytical tools for the determination of elements, such as As, Sb, Bi, Se, Te,Ge, Sn and Pb. Normally, the hydride is generated by the reaction between an acidic sample solution with tetrahydroborate. However, when some inorganic ions such as the transition metal ions are present in the reaction matrix, interference arise. Some approaches for minimizing the interference have been suggested, including the addition of various reagents such as thiourea and iron(III) solution. Interfering metals can also be removed by precipitation. The procedure involved filtration before the solution was acidified. In order to reduce the steps of the process, hydride generation from alkaline solution was described for the determination of selenium in copper and nickel materials.     

贵金属及其掺杂团簇与甲烷反应研究进展

贵金属在甲烷活化与转化中呈现出优良的反应性。研究气态条件下贵金属物种与甲烷的反应,可以从分子水平上揭示凝聚相贵金属催化体系的活性位点与基元反应机理,为理性设计和改进催化剂提供理论基础。本文综述了贵金属原子、离子、团簇、氢化物、卤化物、氧化物、甲基配合物以及掺杂团簇活化、转化甲烷取得的新进展,并针对不同贵金属体系的甲烷活化机理展开讨论。     

Effects of room-temperature ionic liquids on the chemical vapor generation of gold: Mechanism and analytical application

To get insight into the mechanism of the effect of room-temperature ionic liquids (RTILs) on the chemical vapor generation (CVG) of noble metals, gold was taken as a model element, and eight RTILs were examined. All the RTILs resulted in 3-24 times improvement in sensitivity for Au, depending on their nature. For the RTILs with identical anion, the RTILs with the cations of short chain exhibited better enhancement effect than those with long alkyl chain length or complex branch chain. For the RTILs with identical cation, the RTILs with Br⁻ gave the best enhancement effect. The formation of ion pairs between the cation of RTILs and the anion species of gold via electrostatic interaction, and/or the substitution of the Cl⁻ in the anion species of gold by the anion of RTILs likely enabled a more effective CVG reaction to occur. The RTILs also facilitated the generation of small bubbles and provided an electrostatic stabilization to protect the unstable volatile gold species and to help fast isolation of volatile gold species from the reaction mixture. 1-Butyl-3-methylimidazolium tetrafluoroborate [C₄mim]Br gave the best improvement in the sensitivity (24 times) among the RTILs studied, and also reduced the interferences from common transition and other noble metals. Based on the enhancement effect of [C₄mim]Br, a novel flow injection-CVG-atomic fluorescence spectrometric method with a detection limit (3s) of 1.9 μg L⁻¹ and a precision of 3.1% (50 μg L⁻¹, RSD, n = 11) was developed for the determination of trace gold in geological samples.     

The efficiency of chemical vapour generation of transition and noble metals

The efficiency data from individual reports on chemical vapour generation (CVG) of transition and noble metals are overviewed with respect to the ways that they were obtained. The values derived from direct measurement of analyte in the gaseous phase or obtained from comparison with other sample introduction techniques reflect well the true chemical vapour generation efficiency. The efficiencies reported this way do not exceed 30%. On the other hand, the percentage efficiency values derived from determination of analyte remaining in the waste liquid, usually in the high tens, can substantially overestimate the efficiency by neglecting the analyte retained within the system.     

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.     

Confinement Effects in Zeolite‐Confined Noble Metals

Confinement of noble nanometals in a zeolite matrix is a promising way to special types of catalysts that show significant advantages in size control, site adjustment, and nano‐architecture design. The beauty of zeolite‐confined noble metals lies in their unique confinement effects on a molecular scale, and thus enables spatially confined catalysis akin to enzyme catalysis. In this Minireview, the confined synthesis strategies of zeolite‐confined noble metals will be briefly discussed, showing the processes, advantages, features, and mechanisms. The confined catalysis carried on zeolite‐confined noble metals will be summarized, and great emphasis will be paid to the confinement effects involving size, encapsulation, recognition, and synergy. Great progress of atomic sites in the size effect, supercage stabilization in the encapsulation effect, site adsorption in the recognition effect, and cascade reaction in the synergy effect are highlighted. This Minireview is concluded with challenges and opportunities in terms of the synthesis of zeolite‐confined noble metals and their applications to design multifunctional catalysts with high catalytic activity, selectivity, and stability.     

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.     

Surface Atomic Regulation of Core–Shell Noble Metal Catalysts

Core–shell noble metal catalysts have gained significant attention in the past few decades, as they not only reduce the use of noble metals effectively but also exhibit unique properties derived from the synergistic effect between core and shell metals. In particular, regulating the surface structure of shells to maximize the atomic utilization efficiency of noble metals is critically important. Controlling the shell thickness of noble metal catalysts at the atomic level as an efficient approach to realize this goal has been attracting growing attention; this approach involves the formation of ultrathin shells (typically 2–6 atomic layers), monolayers, or even atomically dispersed noble metals embedded in the host metal. These strategies drive the core/support metals to improve the number of active sites and the intrinsic activity of the deposited noble metals remarkably, meanwhile minimizing the usage of noble metals. Herein, recent advances regarding atomic control of the core–shell noble metal catalysts is reviewed, with focus on the surface regulation. First, synthesis methods and surface structures are summarized, and then catalytic applications of these architectures are highlighted.     

Recent Progress of Transition Metal Compounds as Electrocatalysts for Electrocatalytic Water Splitting

Hydrogen has enormous commercial potential as a secondary energy source because of its high calorific value, clean combustion byproducts, and multiple production methods. Electrocatalytic water splitting is a viable alternative to the conventional methane steam reforming technique, as it operates under mild conditions, produces high-quality hydrogen, and has a sustainable production process that requires less energy. Electrocatalysts composed of precious metals like Pt, Au, Ru, and Ag are commonly used in the investigation of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Nevertheless, their limited availability and expensive cost restrict practical use. In contrast, electrocatalysts that do not contain precious metals are readily available, cost-effective, environmentally friendly, and possess electrocatalytic performance equal to that of noble metals. However, considerable research effort must be devoted to create cost-effective and high-performing catalysts. This article provides a comprehensive examination of the reaction mechanism involved in electrocatalytic water splitting in both acidic and basic environments. Additionally, recent breakthroughs in catalysts for both the hydrogen evolution and oxygen evolution reactions are also discussed. The structure-activity relationship of the catalyst was deep-going discussed, together with the prospects of current obstacles and potential for electrocatalytic water splitting, aiming at provide valuable perspectives for the advancement of economical and efficient electrocatalysts on an industrial scale.     

Enrichment of trace amounts of gold, silver, palladium and platinum by precipitate flotation

Summary An organic precipitant, p-dimethylaminobenzilidenerhodanine (DABR), is used as the gatherer in precipitate flotation to enrich trace amounts of gold, silver, palladium and platinum from acidic media in the presence of surfactants. The DABR dissolved in dimethylformamide (DMF) does not affect the determination of the enriched metals with electrothermal atomic absorption spectrometry. The presence of a 10²- to 10⁴-fold excess of other usual ions does not interfere with the flotation owing to the high selectivity of DABR for the noble metals in acidic media. As little as 1 ng/l of gold in aqueous solution can thus be determined by AAS. The method has been applied to determine the noble metals in various ore samples with satisfactory results.Dedicated to Prof. Kuang Lu Cheng, University of Missouri, Kansas City, USA on the occasion of his 70th birthdayPresented in part at the Third China-Japan Joint Symposium on Analytical Chemistry, Hefei, China, May, 1988     

Ermittlung optimaler Meßbedingungen für die atomabsorptions-spektroskopische Bestimmung von Edelmetallen

The parameters for the determination of noble metals by atomic absorption technique are optimized by minimizing of the coeffizients of variation. The optimal conditions for the determination of the elements Ag, Au, Ir, Pd, Pt, Rh and Ru are given.     

Ermittlung optimaler Meßbedingungen für die atomabsorptions-spektroskopische Bestimmung von Edelmetallen

The parameters for the determination of noble metals by atomic absorption technique are optimized by minimizing of the coeffizients of variation. The optimal conditions for the determination of the elements Ag, Au, Ir, Pd, Pt, Rh and Ru are given.     

Trends in sorption preconcentration combined with noble metal determination.

Nowadays much attention is being paid to the determination of trace amounts of noble metals in geological, industrial, biological and environmental samples. The most promising techniques, such as inductively coupled plasma atomic emission spectrometry (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS) and electrothermal atomic absorption spectrometry (ETAAS) are characterized by high sensitivity. However, the accurate determination of trace noble metals has been limited by numerous interferences generated from the presence of matrix elements. To decrease, or eliminate, these interferences, the sorption preconcentration of noble metals is often used prior to their instrumental detection. A great number of hyphenated methods of noble metal determination using sorption preconcentration have been developed. This review describes the basic types of available sorbents, preconcentration procedures and preparations of the sorbent to the subsequent determination of noble metals. The specific features of instrumental techniques and examples of ETAAS, FAAS, ICP-AES, ICP-MS determinations after the sorption preconcentration of noble metals are considered. The references cited here were selected mostly from the period 1996 - 2006.     

Some noble metals and copper content of italian meteorites as determined by destructive neutron activation analysis

Copper, iridium, platinum and gold content was determined in 15 italian chondritic meteorites by destructive neutron activation analysis. The chemical procedure involves few steps: sample dissolution, group separation of noble metals on inorganic adsorbers and gamma-ray spectrometry. Element content and atomic abundances (Si=10⁶ atoms) are presented and discussed. Precision and accuracy of the analytical method are given as well. Copper, platinum and gold content is within the reported ranges for ordinary chondrites, whereas the iridium content is located on the low side of reported values.     

Prediction of a Neutral Noble Gas Compound in the Triplet State

Discovery of the HArF molecule associated with H?Ar covalent bonding [Nature, 2000 , 406, 874–876] has revolutionized the field of noble gas chemistry. In general, this class of noble gas compound involving conventional chemical bonds exists as closed‐shell species in a singlet electronic state. For the first time, in a bid to predict neutral noble gas chemical compounds in their triplet electronic state, we have carried out a systematic investigation of xenon inserted FN and FP species by using quantum chemical calculations with density functional theory and various post‐Hartree–Fock‐based correlated methods, including the multireference configuration interaction technique. The FXeP and FXeN species are predicted to be stable by all the computational methods employed in the present work, such as density functional theory (DFT), second‐order Møller–Plesset perturbation theory (MP2), coupled‐cluster theory (CCSD(T)), and multireference configuration interaction (MRCI). For the purpose of comparison we have also included the Kr‐inserted compounds of FN and FP species. Geometrical parameters, dissociation energies, transition‐state barrier heights, atomic charge distributions, vibrational frequency data, and atoms‐in‐molecules properties clearly indicate that it is possible to experimentally realize the most stable state of FXeP and FXeN molecules, which is triplet in nature, through the matrix isolation technique under cryogenic conditions.     

Neutron activation method in the analysis of geological materials for noble metals

The paper is concerned with various applications of the neutron activation method in the analysis of geological samples for noble metals. A technique is suggested to estimate a priori detection limit values for noble metals in the nondestructive analysis of various samples. Also discussed are new schemes of separation and isolation of elements, the technique of obtaining comparison standards, and constraining factors in application of the method in terms of representation of samples to be analyzed.     

金属离子的光催化去除研究进展

利用光催化剂表面的光生电子或空穴等活性物种，通过还原或氧化反应去除水相中的金属离子，是与环境保护、贵金属回收或金属担载催化剂制备相关的重要过程。笔者结合半导体的结构特征，综述了利用光催化还原反应或氧化反应，对铬、汞、铜、镍、银及铂、钯等贵金属和锰、铀等的光催化去除效果，介绍了该技术在处理金属离子混合体系实现金属分离过程的应用。结合有关实验数据，对一些可能反应机制进行了探讨。对与环境保护及其它相关工艺过程的应用进行了介绍。