正交试验法优选石墨炉测定大米中镉的实验条件

利用L16(45)正交试验设计,考察了石墨炉原子吸收法测定大米中镉的灰化温度、灰化时间、原子化温度、原子化时间.确定了最佳灰化温度为450℃、灰化时间为15s、原子化温度为1750℃、原子化时间为4s等仪器的最佳参数.     

相对峰吸收法测定几种元素在乙炔-空气火焰中的原子化度

本文提出以相对峰吸收法测定元素在乙炔-空气火焰中的原子化度,并讨论了方法的理论基础。采用Cu作参考元素,测定了Na、Mg、Cr和Mo等元素在乙炔-空气火焰中的原子化度。另外,还研究了火焰组成和测量高度对四种元素的吸光度的影响,以及对Na和Mg的原子化度的影响。实验表明,这两个因素对原子化度都有影响,而火焰组成的影响较大。所以,原子化度是一个相对的数值,它与测量条件有密切关系。     

Electrothermal behavior of sodium,potassium, calcium and magnesium in a tungsten coil atomizer and review of interfering effects

The electrothermal behavior of Na, K, Ca and Mg in a 150-W tungsten coil atomizer was investigated in order to gather information about the atomization processes and the underlying factors responsible for chemical interferences of them on atomization of Al, Ba, Cd, Co, Cr, Pb and Yb. The interference effects were discussed considering the thermal stability of the species that could be formed in the condensed phase, the effect of protective gas composition in the atomization process and the pyrolysis temperature curves. Ca is the most serious interferent due to its high thermal stability (up to 1600°C) and to the possibility of double oxides formation. As hydrogen is decisive for the atomization of Na, K, Ca and Mg, some interference processes caused by these elements seem to be related to the competition towards hydrogen present in the protective gas composition. The knowledge of the correct temperature of the tungsten coil surface shows that most strategies for overcoming interferences based on chemical modifiers will fail for Cd and Pb, because tungsten acts as a natural permanent chemical modifier. It seems that in many applications previous separation and masking will be necessary.     

石墨炉原子吸收法中磷酸二氢铵对镉灰化及原子化行为的影响

石墨炉原子吸收法中磷酸二氢铵对镉灰化及原子化行为的影响戴青山，姚金玉，谢文兵，王国平（中国科学院长春应用化学研究所长春１３００２２）关键词石墨炉原子吸收法，动力学模型，Ａｒｒｈｅｎｉｕｓ图镉是易挥发性元素，在石墨炉原子吸收法中，灰化温度为３００℃左右...     

Direct determination of lead in bovine liver by solid sampling with graphite furnace atomic absorption spectrometry—a comparison of tube wall atomization, platform atomization and probe atomization

A comparative study of three atomization techniques is presented: tube wall atomization, platform atomization and probe atomization, in graphite furnace atomic absorption spectrometry for direct determination of lead in bovine liver. Also presented is the effect of oxygen ashing on the lead atomic absorption signal and on the background absorption due to the organic matrix of bovine liver. Study of the lead atomic absorption pulses given by the three atomization techniques using a detection system having a short time constant relative to the atomization and the residence time of lead from Bovine Liver, SRM No. 1577, has provided a new insight into the atomization processes involved in the techniques. The importance of isothermal atomization in reducing or eliminating matrix interferences and the role of oxygen gas in the ashing cycle are presented and discussed.     

Investigation of interference mechanism of cobalt chloride on the determination of bismuth by electrothermal atomic absorption spectrometry

The interferences of cobalt chloride on the determination of bismuth by electrothermal atomic absorption spectrometry (ETAAS) were examined using a dual cavity platform (DCP), which allows the gas-phase and condensed phase interferences to be distinguished. Effects of pyrolysis temperature, pyrolysis time, atomization temperature, heating rate in the atomization step, gas-flow rate in the pyrolysis and atomization steps, interferent mass and atomization from wall on sensitivity as well as atomization signals were studied to explain the interference mechanisms. The mechanism proposed for each experiment was verified with other subsequent sets of experiments. Finally, modifiers pipetted on the thermally treated sample+interferent mixture and pyrolyzed at different temperatures provided very useful information for the existence of volatilization losses of analyte before the atomization step. All experiments confirmed that when low pyrolysis temperatures are applied, the main interference mechanisms are the gas-phase reaction between bismuth and decomposition products of cobalt chloride in the atomization step. On the other hand, at elevated temperatures, the removal of a volatile compound formed between analyte and matrix constituents is responsible for some temperature-dependent interferences, although gas-phase interferences still continue. The experiments performed with colloidal palladium and nickel nitrate showed that the modifier behaves as both a matrix modifier and analyte modifier, possibly delaying the vaporization of either analyte or modifier or both of them.     

Electrothermal atomic-absorption spectrometry of antimony by use of a molybdenum micro-tube atomizer

Electrothermal atomization of antimony has been investigated to clarify the atomization characteristics and interferences from diverse elements, for accurate determination of traces of antimony. Thiourea served to lower the atomization temperature of antimony and to improve the sensitivity. Germanium and phosphoric acid were found to have a pronounced effect on atomization of antimony. The interference of various elements was suppressed in the presence of thiourea. A method involving extraction for determining antimony in metallurgical and geological samples is described.     

Local effects of atomizing analyte droplets on the plasma parameters of the inductively coupled plasma

Monodisperse droplets from aqueous analyte solutions with selected diameters in the range 35–67 µm are introduced into an inductively coupled plasma with frequencies between 1 to 10 droplets per second. The effect of desolvation and atomization in the ICP is studied end-on by optical emission spectroscopy employing simultaneously up to three calibrated monochromators with fast photomultipliers. The onsets of desolvation and analyte atomization and the extremely fast diffusion of hydrogen in the ICP and its effect on the plasma are studied by simultaneous measurements of hydrogen, analyte and Ar lines. The local cooling by analyte atomization as well as the recovering of the plasma excitation temperature after completed atomization is measured quantitatively in dependence on time applying the Boltzmann plot method to simultaneously recorded line intensities of atomized analyte atoms which act as plasma probes. Furthermore, it is shown that relatively small differences in analyte mass cause significant temperature changes during atomization and, as consequence, strong variations of the emission intensity of analyte lines during atomization if measured by end-on observation.     

Effect of atomizer surface type on the quantitation of molybdenum and ytterbium by electrothermal atomization atomic absorption spectrometry

The effect of pyrocoated graphite, uncoated graphite, metal-carbide, and metal atomization surfaces on the quantitation of molybdenum and ytterbium by electrothermal atomization atomic absorption spectrometry was investigated. The peak shape was affected by heating rate and the different surfaces gave different shapes. Except for the case of uncoated graphite, the sensitivities and detection limits were similar for all surfaces. In a sodium chloride matrix it is preferable to use uncoated graphite for molybdenum because an ashing stage greater than the boiling point of sodium chloride can be used without loss of molybdenum. Tube lifetime depended on atomization temperature, atomization time and the matrix.     

Internal standard method in flame atomic absorption spectrometry

Some selection criteria and experimental considerations for selecting an internal standard in flame atomic absorption spectrometry were studied. Rational criteria for the selection of internal standards include the atomization efficiencies of the elements. An experimental study of the variation of the atomization degree due to a temperature decrease can be made with the help of plots of absorbance against the rate at which the sample solution is introduced. The temperature decrease produced by increasing the rate at which water was introduced using a heated chamber without water-cooled condenser was estimated to vary from 2420 K to 2218 K with 1.0 ml water per minute. Curves for the alkali, alkaline earth, and several other metals were obtained in the air-acetylene flame. The shapes of the curves are critically dependent on the degree of atomization of the metal itself. Elements with curves that have similar slopes can be used as mutual internal standards. Some of the other factors which affect the atomization efficiencies—i.e. changes in fuel and air flow, and matrix composition—were also studied.     

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.     

The limitations of Slater's element-dependent exchange functional from analytic density-functional theory

Our recent formulation of the analytic and variational Slater-Roothaan (SR) method, which uses Gaussian basis sets to variationally express the molecular orbitals, electron density, and the one-body effective potential of density-functional theory, is reviewed. Variational fitting can be extended to the resolution of identity method, where variationality then refers to the error in each two-electron integral and not to the total energy. However, a Taylor-series analysis shows that all analytic ab initio energies calculated with variational fits to two-electron integrals are stationary. It is proposed that the appropriate fitting functions be charge neutral and that all ab initio energies be evaluated using two-center fits of the two-electron integrals. The SR method has its root in Slater's Xalpha method and permits an arbitrary scaling of the Slater-Gàspàr-Kohn-Sham exchange-correlation potential around each atom in the system. The scaling factors are Slater's exchange parameters alpha. Of several ways of choosing these parameters, two most obvious are the Hartree-Fock (HF) alpha(HF) values and the exact atomic alpha(EA) values. The former are obtained by equating the self-consistent Xalpha energy and the HF energies, while the latter set reproduces exact atomic energies. In this work, we examine the performance of the SR method for predicting atomization energies, bond distances, and ionization potentials using the two sets of alpha parameters. The atomization energies are calculated for the extended G2 set of 148 molecules for different basis-set combinations. The mean error (ME) and mean absolute error (MAE) in atomization energies are about 25 and 33 kcal/mol, respectively, for the exact atomic alpha(EA) values. The HF values of exchange parameters alpha(HF) give somewhat better performance for the atomization energies with ME and MAE being about 15 and 26 kcal/mol, respectively. While both sets give performance better than the local-density approximation or the HF theory, the errors in atomization energy are larger than the target chemical accuracy. To further improve the performance of the SR method for atomization energies, a new set of alpha values is determined by minimizing the MAE in atomization energies of 148 molecules. This new set gives atomization energies half as large (MAE approximately 14.5 kcal/mol) and that are slightly better than those obtained by one of the most widely used generalized-gradient approximations. Further improvements in atomization energies require going beyond Slater's functional form for exchange employed in this work to allow exchange-correlation interactions between electrons of different spins. The MAE in ionization potentials of 49 atoms and molecules is about 0.5 eV and that in bond distances of 27 molecules is about 0.02 A. The overall good performance of the computationally efficient SR method using any reasonable set of alpha values makes it a promising method for study of large systems.     

Investigation of phosphorus atomization using high-resolution continuum source electrothermal atomic absorption spectrometry

The atomization of phosphorus in electrothermal atomic absorption spectrometry has been investigated using a high-resolution continuum source atomic absorption spectrometer and atomization from a graphite platform as well as from a tantalum boat inserted in a graphite tube. A two-step atomization mechanism is proposed for phosphorus, where the first step is a thermal dissociation, resulting in a fast atomization signal early in the atomization stage, and the second step is a slow release of phosphorus atoms from the graphite tube surface following the adsorption of molecular phosphorus at active sites of the graphite surface. Depending on experimental conditions only one of the mechanisms or both might be active. In the absence of a modifier and with atomization from a graphite or tantalum platform the second mechanism appears to be dominant, whereas in the presence of sodium fluoride as a modifier both mechanisms are observed. Intercalation of phosphorus into the graphite platform in the condensed phase has also been observed; this phosphorus, however, appears to be permanently trapped in the structure of the graphite and does not contribute to the absorption signal.     

元素在石墨炉内石墨探针表面上的原子化机理研究(X)——硝酸锶的原子化机理

用X射线衍射、X射线光电子能谱、俄歇电子能谱和扫描电子显微术等考察了石墨炉升温过程中Sr(NO₃)₂在石墨探针表面上的形态变化,阐明了它的原子化机理.加热过程中Sr(NO₃)₂首先分解为SrO(s),再还原为SrC₂,后者进一步分解为Sr(s).锶的原子化源于金属蒸发.     

Lead atomization in the presence of aluminum matrices by electrothermal atomic absorption spectrometry. A comparative study of slurry vs solution sample introduction

The atomization behaviour of Pb introduced to the electrothermal atomizer in a slurry of Al₂O₃ and in a solution of Al(NO₃)₃ has been studied. The characteristics of the absorbance vs time profiles are highly dependent on the way in which Pb is incorporated in the matrix. In particular, Pb adsorbed on the surface of Al₂O₃ particles behaves differently from Pb entrapped within the particles. Atomization using platform and wall atomization from both pyrolytic and non-pyrolytic graphite surfaces is described. Pyrolytic platforms do not always provide complete recovery and better results are obtained with atomization from a non-pyrolytic platform surface within a pyrolytically coated tube. With wall atomization, large differences in the absorbance vs time profiles precludes its use for quantitative determinations. However, wall atomization should be useful for future studies of the kinetic and thermodynamic processes of Pb release. Finally, the feasibility of using the non-resonance Pb line at 261.4 nm to reduce the analytical sensitivity is examined. The strong dependence of the lower energy level population on temperature makes this difficult, but the absorbance profiles with non-pyrolytic platform atomization show that all forms of Pb can be made to atomize at similar temperatures.     

元素在石墨炉内石墨探针表面上的原子化机理研究(Ⅰ)——镉与铝的原子化机理

自1978年B.V. L′vov提出石墨炉内探针原子化技术以来,许多作者对该技术进行了研究,并将其应用于实际样品的测定,国内亦有人作过系统的评述,但对元素在石墨探针表面上的原子化机理却报道不多。本文应用X射线衍射分析与其它一些实验,观察和研究了镉和铝在石墨探针表面上原子化过程中的形态变化,阐明了镉和铝的原子化历程。     

石墨炉内石墨探针表面原子化机理的研究：Ⅳ.硝酸铕的原子化机理

用Ｘ－射线衍射分析与Ｘ－射线光电子能谱分析研究了硝酸铕在石墨炉内石墨探针表面原子化机理。研究结果表明，在硝酸铕的原子化过程中，Ｅｕ（ＮＯ３）３先转化Ｅｕ２Ｏ３，生成的Ｅｕ２Ｏ３经一系列的晶型转变之后，热分解为ＥｕＯ（ｓ），后者以ＥｕＯ（ｇ）形式蒸发进入气相。硝酸铕的原子化起源于ＥｕＯ（ｇ）的热分解。在１６６０Ｋ和１９２０Ｋ时有铕的碳化物ＥｕＣ２生成。     

Effect of matrix components on chromium atomization processes in graphite furnace atomic absorption spectrometry

The effect of various organic and inorganic matrix components on chromium atomization in graphite furnace atomic absorption spectrometry is studied. The results are explained on the basis of chromium's atomization mechanisms. The two predominant mechanisms are the thermal dissociation of the oxide and of the carbide. Losses through molecular volatilization reduce the sensitivity when chromium chelate complexes are atomized. In this case, the atomization mechanism consists of the thermal dissociation of the chelate. The formation of chromium carbide from the carbon residue produced by decomposition of the organic solvents leads to a loss of sensitivity.     

Atomic absorption spectrometry of germanium with a tungsten electrothermal atomizer

The electrothermal atomization of germanium in a metal micro-tube atomizer is described. Tungsten is preferable to other metals for the atomizer. Hydrogen lowers the atomization temperature of germanium, and improves the sensitivity for germanium significantly when the optimum flow rates are applied. There are pronounced interferences from diverse elements and acids on the atomization of germanium. A procedure which involves carbon tetrachloride extraction of germanium tetrachloride and back-extraction of germanium into water avoids many of the interferences and is recommended for rock samples.