有机试剂对锶火焰原子吸收光谱分析的增感机理

研究了火焰原子吸收光谱法中甲醇、甲醛、甲酸等6种有机试剂对元素Sr的增感行为,发现甲酸效果最佳。在选定的相对最佳条件下,增感效果高达70%。研究表明,甲酸所产生的增感效应主要在于其与Sr形成甲酸锶,改变了常规原子化机理,提高了火焰原子化效率。这一机理同样适用于甲酸存在下Ca、Ba等元素的火焰原子化。实验表明,甲酸对这两种碱土元素的增感效果分别达到54%和55%。甲酸对Sr的增感应用于高纯BaCO3中Sr含量测定,回收率达到100%～106%。     

Hydride atomization in a cool hydrogen—oxygen flame burning in a quartz tube atomizer

A method of selenium hydride atomization using a cool highly fuel rich-hydrogen—oxygen diffusion flame burning in the inlet part of a T-shaped quartz tube placed in the optical axis of an atomic absorption spectrometer is investigated. It is shown that hydride atomization is caused by free radicals (H, OH) generated in the flame. Atomization (proceeding probably with 100% efficiency) is completed before the gases reach the optical axis. The life-time of free radicals is considerably reduced by admixture of even small amounts of oxygen to the hydrogen flush gas.A mathematical function describing the dependence of the selenium peak areas on the gas flow is derived and values for the selenium atomic absorption coefficient and rate constant for selenium decay by reactions on the tube walls are obtained by fitting experimental data to this function. The atomic absorption coefficient agrees well with a theoretically estimated value. The described method seems promising for absolute analysis by AAS.     

低温原子化石墨炉原子吸收法测定环境和生物样中的镉

本文描述了以氩/氢混合气体作保护气体,测定环境和生物样品中痕量镉的石墨炉原子吸收法。实验证明,与纯氩气作保护气体相比较用氩/氢混合气体作保护气体,能够降低镉的原子化温度(100℃),并且减少基体物质如MgCl_2和NaClO_4的干扰。这种改善氯化物和高氯酸盐基体干扰的机理,主要是由于氢的存在与基体中的氯形成高离解能的氯化氢,从而避免了通常在镉原子化之前形成易挥发的氯化镉而损失。用本方法测定了七种标准参考物质,结果与标准值一致,证明方法是可靠的。     

Nickel and strontium nitrates as modifiers for the determination of selenium in wine by Zeeman electrothermal atomic absorption spectrometry

A mixed matrix modifier of nickel and strontium nitrates was used as a chemical modifier for the determination of selenium in wines by Zeeman electrothermal atomic absorption spectrometry. Wine samples were heated on a boiling water bath with small amounts of nitric acid and hydrogen peroxide. For complete elimination of interference, especially from sulfates and phosphates, selenium is complexed with ammonium pyrolidinedithiocarbamate (APDTC), extracted into methyl isobutyl ketone (MIBK), and measured by ETAAS. The graphite furnace temperature program was optimized for both aqueous and organic solutions. Pyrolysis temperatures of 1300 degrees C and 800 degrees C were chosen for aqueous and organic solutions, respectively; 2700 degrees C and 2100 degrees C were used as optimum atomization temperatures for aqueous and organic solutions, respectively. The optimum modifier mass established is markedly lower than those presented in the literature. The platform atomization ensures pretreatment stabilization up to 1100 degrees C and 1600 degrees C, respectively, for organic and aqueous selenium solutions. The procedure was verified by the method of standard addition. The investigated wine samples originated from the different regions of the Republic of Macedonia. The selenium concentration varied from not detectable to 0.93 microg L(-1).     

Nickel and strontium nitrates as modifiers for the determination of selenium in wine by Zeeman electrothermal atomic absorption spectrometry

A mixed matrix modifier of nickel and strontium nitrates was used as a chemical modifier for the determination of selenium in wines by Zeeman electrothermal atomic absorption spectrometry. Wine samples were heated on a boiling water bath with small amounts of nitric acid and hydrogen peroxide. For complete elimination of interference, especially from sulfates and phosphates, selenium is complexed with ammonium pyrolidinedithiocarbamate (APDTC), extracted into methyl isobutyl ketone (MIBK), and measured by ETAAS. The graphite furnace temperature program was optimized for both aqueous and organic solutions. Pyrolysis temperatures of 1300?°C and 800?°C were chosen for aqueous and organic solutions, respectively; 2700?°C and 2100?°C were used as optimum atomization temperatures for aqueous and organic solutions, respectively. The optimum modifier mass established is markedly lower than those presented in the literature. The platform atomization ensures pretreatment stabilization up to 1100?°C and 1600?°C, respectively, for organic and aqueous selenium solutions. The procedure was verified by the method of standard addition. The investigated wine samples originated from the different regions of the Republic of Macedonia. The selenium concentration varied from not detectable to 0.93 μg L^–1.     

Determination of thallium by electrothermal atomic absorption spectrometry with a metal atomizer

Summary Electrothermal atomization of thallium in a molybdenum microtube atomizer is described. The addition of a low flow rate of hydrogen to argon purge gas resulted in higher peak absorption. In the presence of thiourea the addition of hydrogen did not alter the peak absorption value in pure argon, although the peak temperature shifted to lower region. A high heating rate of the atomizer was recommended for higher peak absorption and improvement of interferences from concomitants. The interferences by concomitants at 50 ng level were modified with thiourea. Modification with thiourea was effective even for interferences from 500 ng of cadmium, zinc or copper, while it was insufficient for 500 ng of calcium, magnesium, chromium, bismuth or lead. Provided the atomization of thallium was carried out at high heating rate and on addition of thiourea as a matrix modifier, the interference from chloride (500 ng) was modified. The absolute sensitivity (0.0044 abs) for thallium was 1.2 pg.

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Thalliumbestitmmung durch AAS mit elektrothermischer Atomisierung in einem metallischen Atomizer

Zusammenfassung Zur AAS-Bestimmung von Thallium wird eine Molybdän-Mikroröhre als Atomizer empfohlen. Zusatz von geringeren Wasserstoffmengen zum Argongas ergab eine höhere Absorption. In Gegenwart von Thioharnstoff erfolgte durch Wasserstoff-Zugabe keine Änderung des Absorptionswertes in reinem Argon, obwohl die Peaktemperatur in einen niederen Bereich verschoben wurde. Für höhere Absorption und zur Verminderung von Störungen durch Begleitelemente wurden höhere Erhitzungsgeschwindigkeiten empfohlen. Störungen durch Begleitelemente im Bereich von 50 ng konnten mit Thioharnstoff verringert werden. Die Zugabe von Thioharnstoff erwies sich ebenfalls als wirksam für 500 ng Cadmium, Zink oder Kupfer, während sie für dieselben Mengen an Calcium, Magnesium, Chrom, Bismut oder Blei ungenügend war. Mit hoher Erhitzungsgeschwindigkeit und Thioharnstoffzusatz konnte eine Störung durch Chlorid im Bereich von 500 ng reduziert werden. Die absolute Empfindlichkeit für Thallium (0,0044 abs) betrug 1,2 pg.

     

Temporal Variations in Gas Temperature in an Atomization Stage of Cadmium and Tellurium Evaluated by Using the Two-line Method in Graphite Furnace Atomic Absorption Spectrometry

In order to discuss the atomization process of an analyte element occurring in a graphite furnace for atomic absorption spectrometry, we measured variations in the characteristic temperature with the progress of an atomization stage, by using a two-line method under the assumption of a Boltzmann distribution. For this purpose, iron was chosen as the analyte element. Also, the atomic absorption of two iron atomic lines, Fe I 372.0 nm and Fe I 373.7 nm, was simultaneously monitored as a probe for the temperature determination. This method enables variations in the gas temperature to be directly traced, yielding a temperature distribution closely related to the diffusion behavior of the probe element in the furnace. This temperature variation was very different from the furnace wall temperatures, which were monitored in conventional temperature control for atomic absorption spectrometry. Correlations between the gas temperature and the charring/atomizing temperatures in the heating program of the furnace were investigated. The atomization of cadmium and tellurium was also investigated by a comparison between the gas temperature with the wall temperature of the furnace. The atomic absorption of cadmium or tellurium appeared to be apart from the absorption of iron while the gas temperature was still low. Therefore, the analyte atoms could be atomized through direct contact with the wall of the graphite furnace, which has a much higher temperature compared to the gas atmosphere during atomization. Their atomization would be caused by conductive heating from the furnace wall rather than by radiant heating in the furnace.     

Organic solvents as interferents in arsenic determination by hydride generation atomic absorption spectrometry with flame atomization

Interference effects of various organic solvents miscible with water on arsenic determination by hydride generation atomic absorption spectrometry have been studied. Arsine was chemically generated in continuous flow hydride generation system and atomized by using a flame atomizer able to operate in two modes: miniature diffusion flame and flame-in-flame. The effects of experimental variables and atomization mode were investigated: tetrahydroborate and hydrochloric acid concentrations, argon, hydrogen and oxygen supply rates for the microflame, and the distance from the atomization region to the observation zone. The nature of the species formed in the flame due to the pyrolysis of organic solvent vapors entering the flame volume together with arsine is discussed. The observed signal depression in the presence of organic solvents has been mainly attributed to the atomization interference due to heterogeneous gas–solid reaction between the free arsenic atoms and finely dispersed carbon particles formed by carbon radicals recombination. The best tolerance to interferences was obtained by using flame-in-flame atomization (5–10 ml min^− 1 of oxygen flow rate), together with higher argon and hydrogen supply rates and elevated observation heights.     

Determination of lanthanum in food and water samples by Zeeman-effect atomic absorption spectrometry using graphite tube lined with tungsten foil.

A sensitive, selective method for the determination of lanthanum in food and water samples by atomic absorption spectrometry using a graphite tube lined with tungsten foil is described. The atomization of lanthanum from the tungsten surface gives better analytical sensitivity, a lower atomization temperature and negligible memory effects. The characteristic mass and detection limit of the method were 8.1 x 10(-9) and 7.85 x 10(-9) g, respectively. The precision (relative standard deviation in the range 5.9-9.9%), accuracy and interferences of the method were also investigated. The method can be used directly for the determination of trace amounts of lanthanum in food and water without pre-dissociation of the matrices. The results obtained by this method are in good agreement with those obtained from inductively coupled plasma atomic emission spectrometry.     

Effect of beryllium nitrate vaporization on surface temperature in the pyrocoated graphite furnace

The vaporization of 20–50 μg beryllium from nitrate solution was observed in graphite furnace atomizers using pyrocoated and Ta-lined tubes. A charge coupled device (CCD) spectrometer was employed to follow the evolution of absorption spectra (200–475 nm), the light scattering and emission. Molecular bands of NO and NO₂ were observed below 1000°C. Beryllium absorption at 234.9 nm was prominent in spectra above 2200°C and 1900°C, respectively, in Ta-lined and pyrocoated tubes. The evolution profile of Be atomic absorption and of some bands indicated a faster vapor release in the pyrocoated tube. Light scattering occurred only in the pyrocoated tube, increasing with the tube age. When purge gas mini flow was applied, the scattering was observed at 1900–2200°C simultaneously with Be atomic absorption and emission continuum at long wavelength. The emission continuum showed the wavelength distribution characteristic of black body radiation. The temperature increase, due to the vaporization of the sample, was estimated using Planck’s equation. The maximum temperature increase reached 400°C, when the most intense Be atomic absorption, light scattering and emission was observed. According to the hypothesis proposed, the black body radiation was induced by the formation of Be carbide in the pyrographite layer. Low heat capacity across the pyrographite prevented the heat dissipation, and led to increase of surface temperature. This induced an increase of sample evaporation rate and the formation of a thermal gradient in the cross section of the tube. Both factors originated vapor supersaturation in the tube center, spatial condensation and, accordingly, light scattering. The results, together with those already obtained with Mg nitrate place limitations to the atomization theories based on the concept of isothermal equilibrium or on Arrhenius kinetic approach.     

Use of Electrolyte Jet Cathode Glow Discharges as Sources of Emission Spectra for Atomic Emission Detectors in Flow-Injection Analysis

Atmospheric glow discharges with electrolyte jet cathodes are proposed as atomization and excitation sources for atomic emission detectors for easily atomized metals in flow-injection analysis. The applicability of these sources to determining potassium, calcium, and sodium in concentration ranges of 0.01–10 mM using a semiconductor photodetector was demonstrated. It was found that the analytical signal enhanced with an increase in the temperature of the solution and a decrease in its flow rate, which was explained by the enhancement of the thermal sputtering of the electrolyte cathode.     

镥、镱基体在石墨炉原子吸收光谱中的背景吸收研究

利用镥、镱基体在石墨炉中的蒸发行为研究了背景吸收的来源 ,讨论利用基体改进剂减少氯化物背景吸收的方法 ,为镥、镱基体中超痕量元素的精确测定提供帮助。     

Spectroscopic study of atomization processes and inter-element effects on the flame emission of chromium and iron in an air—acetylene flame

Emission spectroscopy is applied for characterization of reactions occurring in air—acetylene flames normally used for atomic absorption spectrometry. Inter-element effects on the emissions of chromium and iron are discussed. Two atomic emission lines with different upper energies and a molecular emission line of the diatomic oxide MO are compared for determination of the excitation temperature and the degree of atomization in fuel-rich and lean flames. The reductive power of the fuel-rich flame is essential for atomization of chromium salts. Inter-element effects by iron can be attributed to the formation of refractory oxides, and to mutual catalytic oxidation.     

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.     

Sampling statistics and considerations for single-shot analysis using laser-induced breakdown spectroscopy

A statistical analysis of single-shot spectral data is reported for laser-induced breakdown spectroscopy (LIBS). Fluctuations in both atomic emission and plasma continuum emission are investigated in concert for a homogenous gaseous flow, and fluctuations in plasma temperature are reported based on iron atomic emission in an aerosol-seeded flow. Threshold irradiance for plasma initiation and plasma absorption were investigated for pure gaseous and aerosol streams, with detailed statistical measurements performed as a function of pulse energy in the breakdown regime. The ratio of the analyte atomic emission intensity to the continuum emission intensity (peak/base) provided a robust signal for single-shot LIBS analysis. Moreover, at optimal temporal delay, the precision of the LIBS signal was maximized for pulse energies within the saturation regime with respect to plasma absorption of incident energy. Finally, single-shot temperature measurements were analyzed, leading to the conclusion that spatial variations in the plasma volume formation and subsequent plasma emission collection, play important roles in the overall shot-to-shot precision of the LIBS technique for gaseous and aerosol analysis.     

Atomic absorption spectrometry of tin with electro-thermal atomization in a molybdenum microtube

The atomic absorption spectrometry of tin with atomization in a molybdenum microtube is described. The addition of hydrogen to the argon purge gas improves the efficiency of atomization of tin; measurements are best done at 224.61 nm. Phosphoric acid lowers the atomization temperature of tin, and depresses the interferences from diverse elements. Tin in canned foods (fruit juices and drinks) can be determined by direct atomization after dilution with phosphoric acid. Prior extraction is necessary for analysis of geological materials.     

Determination of calcium, magnesium and zinc in unused lubricating oils by atomic absorption spectroscopy

Varying concentrations of lanthanum and strontium were added to solutions of ashed unused lubricating oils for the determination of calcium, magnesium and zinc content using flame atomic absorption spectrophotometry. At least 3000 μg g⁻¹ of lanthanum or strontium was required to completely overcome the interference of the phosphate ion, PO³⁻₄, and give peak values for calcium. The presence of lanthanum or strontium did not cause an appreciable increase in the amount of magnesium and zinc obtained from the analyses. The method is fast and reproducible, and the coefficients of variation calculated for the elements using one of the samples were 1.6% for calcium, 3.5% for magnesium and 0.2% for zinc. Results obtained by this method were better than those obtained by other methods for the same samples.     

Determination of strontium in human tooth enamel by atomic absorption spectrometry

Interferences in the atomic absorption of strontium by calcium and phosphate at the levels found in human tooth enamel were investigated for both air-acetylene and nitrous oxide-acetylene flames. In air-acetylene flames, the interferences can be reduced by the addition of lanthanum(III); but perchloric acid, used for sample dissolution, causes a significant reduction in the calcium-phosphate interference, so that a standard addition method can be applied, without the need for any chemical separations. An average recovery of 98.6% for added amounts of strontium to enamel showed the proposed method to be reliable.     

Interferences in hydride atomization studied by atomic absorption and atomic fluorescence spectrometry

A hydride atomizer able to operate in the flame-in-tube mode and in the miniature diffusion flame mode was used to investigate interferences of arsenic in selenium atomization. A twin-channel continuous flow hydride generator was utilized to eliminate liquid phase interferences. Both atomic absorption and atomic fluorescence detectors (EDL sources) were employed. The miniature diffusion flame can tolerate interferent concentrations up to 70 μg ml⁻¹. The magnitude of interferences in the flame-in-tube atomizer is controlled by the distance between the atomization and detection zones. The best tolerance to interferents, comparable with that in the miniature diffusion flame, was obtained for the minimum distance of the zones. The figures were deteriorated by two orders of magnitude when increasing the distance between the observation and the atomization zones to 50 mm. Also a curvature and rollover of calibration graphs was observed when increasing the distance. The presence of the interferent enhanced substantially the curvature and rollover, so that the magnitude of observed interferences was dependent on the analyte concentration. All the observed interferences and the calibration graph curvature are due to the decay of free analyte atoms by reactions in the free space. The nature of the species formed is discussed. No significant depletion of hydrogen radicals was observed. As demonstrated by measurements in the miniature diffusion flame, the species formed can be reatomized by interaction with hydrogen radicals with an efficiency better than 90%.     

Fundamental studies of mixed-gas inductively coupled plasmas

The effects of adding foreign gases to the central-gas flow or the intermediate-gas flow of an argon inductively coupled plasma are presented. In particular, the influence of up to 16.7% added helium, nitrogen or hydrogen on radially-resolved electron number density, electron temperature, gas-kinetic temperature and calcium ion emission profiles is examined. It is shown that these gases affect not only the fundamental parameters and bulk properties of the plasma, but also how energy is coupled and transported through the discharge and how that energy interacts with the sample. For example, added helium causes an increase in the gas-kinetic temperature, most likely due to the higher thermal conductivity of helium compared to argon but, in general, does not appear to affect significantly either the electron temperature or electron concentration. The shift in the calcium ion emission profile towards lower regions in the discharge with added helium may be attributable to higher droplet desolvation and particle vaporization rates. In contrast, the addition of nitrogen or hydrogen to an Inductively Coupled Argon Plasma (Ar ICP) results in dramatic changes in all three fundamental plasma parameters: electron number density, electron temperature, and gas-kinetic temperature. The net effect of these molecular gases (N₂ or H₂) on calcium ion emission and on the fundamental plasma parameters is shown to be dependent on the amount of gas added to the plasma and whether the gas is introduced as part of the central- or intermediate-gas flow. In general, nitrogen added to the central-gas flow causes a significant reduction in the number of electrons throughout most of the discharge (over an order of magnitude in certain regions), mainly in the central and upper zones of the ICP. A drop of 3000–5000 K in the central channel electron temperature and a smaller drop in the gas-kinetic temperature are also observed when N₂ is added to the central-gas flow. In contrast, the introduction of nitrogen in the intermediate flow causes about a 1 × 10¹⁵ electrons cm⁻³ increase in the electron concentration in the low, toroidal regions of the plasma and an increase in the gas-kinetic temperature of around 1000 K throughout most of the discharge. As seen with the addition of nitrogen to the central-gas flow, the electron temperature is found to increase in the toroidal zones of the plasma when N₂ is added to the intermediate flow. These combined effects cause a 20-fold depression in the calcium ion emission intensity only a 1.7-fold depression when N₂ is added to the central- or intermediate-gas flows, respectively. On the other hand, hydrogen causes a depression in the electron concentration in the upper areas of the plasma when this gas is added to the central flow but increases the number of electrons in the same region when added to the intermediate flow. Hydrogen also causes a dramatic effect on the electron and gas-kinetic temperatures, significantly increasing both of these parameters throughout the discharge. An increase in the calcium ion emission intensity, accompanied by a downward shift, elongation and broadening of the calcium ion emission profile is also observed with H₂ addition.