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.     

Non-spectral interferences in flameless atomic absorption spectrometry using graphite mini-tube furnaces

This work concerns non-spectral interferences occurring in flameless atomic absorption spectrometry using a Varian Techtron CRA model 63 instrument. Special attention has been paid to the influence exerted by concomitants on the vaporization and atomization behaviour of the test elements Be, Mn and Zn. Tracer analysis permitted the direct determination of the vaporization patterns of the test elements during the atomization phase. The variation of the transient absorption signals with time was measured using an electronic recording system sufficiently fast to obtain instrumentally undistorted pulses. The concomitants were selected on the basis of literature dealing with thermochemical processes in are emission spectrometry. Results are discussed on the basis of (i) the decrease of the content of the test element in the furnace, (ii) the characteristics of the absorption signal, and (iii) the surface temperature of the furnace. It turned out that the class “atomization efficiency interferences” might constitute one of the most serious sources of systematic error in frameless atomic absorption spectrometry.     

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.     

Ascorbic acid as a matrix modifier for determination of tin in concentrated boric acid solutions by electrothermal atomic-absorption spectrometry

It has been found that the atomic-absorption signal for tin is reduced in the presence of 5 micro1 of 0.05-0.30M boric acid at STPF-conditions. It has been proposed that the reason for the boron interferences is the formation of SnB(g) at the atomization stage. In the presence of palladium chloride the interferences from 0.2M boric acid are reduced by a factor of 1.3. The interferences are reduced most effectively when the sample is atomized from a polycrystalline graphite platform or in the presence of ascorbic acid. The interference of up to 0.2M boric acid can be suppressed and the area of the tin signal doubled. It is proposed that the observed phenomenon is connected with the bonding of boron as non-volatile B(4)C. Ascorbic acid is the most effective matrix modifier for the determination of different trace elements in boron compounds.     

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.     

Molecular emission cavity analysis13-a new flame analytical technique : Part II.The determination of selenium and tellurium

The determination of 0.4–4 μg of selenium by molecular emission cavity analysis is described. Selenium in organic compounds is determined after oxygen flask combustion. Metal ion interferences are eliminated by reduction of selenium to the element, filtration onto a glass-fibre paper, and direct incorporation of the filter into the cavity. Applications to the determination of selenium in inorganic and organic compounds are described. The determination of μg-amounts of tellurium is also outlined.     

Determination of trace quantities of selenium by indirect atomic-absorption spectrophotometry

The selenium(IV)-iodide interaction in acid medium, leading to the liberation of iodine, has been utilized for the indirect determination of selenium by atomic-absorption spectrophotometry (AAS). The iodine is extracted into benzene and subsequently reductively stripped into an aqueous solution of ascorbic acid. After extraction of the resulting iodide as tris(1,10-phenanthroline)cadmium(II) iodide into nitrobenzene, the cadmium content of the organic extract is determined by AAS. Beer's law is applicable up to 0.75 ppm of selenium. The few interferences are readily overcome. The chemical yield in the system is about 80% overall.     

Influence of volatile hydride-forming elements on antimony determination by atomic-absorption spectrometry with hydride-generation

A study was undertaken to determine the interfering effects of arsenic, bismuth, germanium, lead, selenium, tin and tellurium on trace determination of antimony by atomic-absorption spectrometry with hydride-generation. A 1% NaBH(4) solution was used as reductant and a small amount of oxygen was added to the hydrogen produced, to support the combustion and atomization of SbH(3). The interference from selenium in the determination of antimony is removed if potassium iodide-ascorbic acid solution or copper sulphate is added to the sample solution. The interference of tin and tellurium can also be avoided by adding potassium iodide-ascorbic acid solution. A possible interference mechanism is discussed.     

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.     

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%.     

Studies in hydride generation atomic fluorescence determination of selenium and tellurium. Part 2 — effect of thiourea and thiols

In determination of selenium and tellurium by continuous flow hydride generation atomic fluorescence spectrometry, the effect of thiourea and thiols was investigated in view of their potential to achieve mild reaction conditions and as masking agents of interference from foreign elements. The effect of thiourea and thiols was first tested in the absence of interfering species and using different addition modes to reaction system. In the absence of interfering species, thiols negatively influenced the hydride evolution of both selenium and tellurium and, in general, they did not produce the desired effects. Thiourea was well tolerated in the determination of both elements by appropriate choice of experimental conditions. Possible mechanisms producing the depressive effect of thiourea and thiols were also investigated and are discussed later. Compromise reaction conditions were identified by using on-line addition of a neutral thiourea solution to acidified sample, combined with KI addition to NaBH₄. Mild reaction conditions can be achieved by decreasing the NaBH₄ concentration but at the expense of a reduced linear dynamic range. In the presence of foreign elements, thiourea allowed good control of interferences generated by Cu(II), Co(II), Ni(II), Au(III), Ag(I) and Bi(III). Tolerance limits could be improved by factors in the range of 7–2000, for both selenium and tellurium determination. The method has been successfully applied in the determination of traces of tellurium and selenium in copper, lead and molybdenum ores, stainless steel and pure copper metal without any additional steps other than sample dissolution.     

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.     

Simultaneous determination of Se and As by hydride generation atomic absorption spectrometry with analyte concentration in a graphite furnace coated with zirconium

Conditions for the simultaneous determination of selenium and arsenic at ng l⁻¹ level were developed. Simultaneous determination of these elements was possible through the multielement capabilities of hydride generation, with in situ trapping and atomization in a graphite tube coated with zirconium and measurements using a dual channel atomic absorption spectrophotometer. The zirconium coating employed in this work was relatively stable; once formed it could stand ≈80 firings without any significant change in the efficiency of hydride collection. This appears to be an advantage over the palladium coating, which is usually formed individually before each measurement because of its thermal instability during the atomization step of the furnace temperature programme. As a result, two determinations of the two elements could be performed in 2.5 min. Under the optimized conditions, concentration detection limits of 17 and 13 ng l⁻¹ for a 7.1 ml sample volume were obtained for selenium and arsenic, respectively (absolute detection limits 120 and 92 pg for Se and As).     

Study of the effects of elements that form volatile hydrides on the determination of selenium by hydride generation atomic absorption spectrometry

Summary A study has been made of possible interferences upon the determination of selenium by hydride generation atomic absorption spectrometry (HGAAS), due to the presence of other hydride forming elements such as As, Ge, Bi, Te, Sn and Sb, and to a volatile element such as Hg. The interfering effects of these cations were determined at several concentration levels using sodium borohydride as the reductant and a commercially available semi-automatic system for the generation and the flameless combustion of the hydrides. It has been demonstrated that the determination of selenium by HGAAS is relatively free from interferences with regard to other elements that form volatile hydrides, except for tin and bismuth that strongly interfere.

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Einfluß von flüchtige Hydride bildenden Elementen auf die Selenbestimmung als Hydrid durch AAS

Zusammenfassung Bei der AAS-Bestimmung von Selen als Hydrid wurde der Einfluß der hydridbildenden Elemente As, Ge, Bi, Te, Sn, Sb sowie auch des flüchtigen Elements Hg untersucht. Die Untersuchungen wurden bei verschiedenen Konzentrationen mit Natriumborhydrid als Reduktionsmittel durchgeführt. Dabei wurde ein handelsübliches halbautomatisches System zur Erzeugung und flammenlosen Verbrennung der Hydride benutzt. Es zeigte sich, daß die Selenbestimmung bis auf die stark störenden Elemente Sn und Bi relativ frei von Beeinflussungen ist.

     

电感耦合等离子体质谱法测定西红柿中微量元素

采用带六极杆碰撞反应池（CCT）的电感耦合等离子体质谱法（ICP-MS）直接测定了蔬菜样品中微量和痕量金属元素。在碰撞反应池中引入He／H2（93／7）混合气,有效地消除了分子离子（ArCl^-、ArAr^＋等）对痕量砷、硒测定的干扰。比较了原子吸收光谱法和原子荧光法测定结果,两种方法获得的结果基本一致。     

Atomic fluorescence analysis with gas-phase atomization in an inductively coupled plasma

A method of analysis is proposed that involves isolation of elements to be determined from a sample in the form of volatile compounds, with their subsequent trapping and final atomic fluorescence determination with gas-phase atomization in an inductively coupled plasma. An air-cooled torch with a low consumption of argon was used as the atomizer. This technique eliminates almost all interferences from both matrix elements and atomizing media, and allows the analysis of a wide range of materials with a spectrometer that is calibrated on pure compounds of the elements to be determined without the need for matrix-matched standard reference materials. The method was applied to multi-element environmental analyses.     

Atomic absorption spectrometry of selenium in an argon-hydrogen flame after electrochemical preconcentration

Different methods of atomization of selenium from a platinum wire filament are described, including electrothermal heating of the filament and atomlzation in an argon-hydrogen flame. A combination of these approaches proved to give the best sensitivity and detection limit. The selenium was preconcentrated on the filament by electrolysis prior to the atomic absorption measurements to eliminate chemical interferences and improve the sensitivity of the method. The detection limit was 0.5 μg l^-1 for a 5-min electrolysis, and 0.2 μg l^-1 when the electrolysis time was 30 min.     

Determination of selenium and tellurium in electrolytic copper by anodic stripping voltammetry at a gold film electrode

A simple procedure for the determination of selenium and tellurium in electrolytic copper is described. These two elements are first separated from copper by passing an ammoniacal solution of the sample through Chelex-100 resin. Voltammetric interferences from nitrite liberated during the dissolution of the metal sample in nitric acid and from arsenic and antimony present in the metal are eliminated by addition of hydrogen peroxide. Excess of peroxide is quickly decomposed by the copper(II) ions present. As little as 0.01 μg Se g^-1 and 0.02 μg Te g^-1 can be determined; relative standard deviations (n = 5) are in the ranges 1.4–3.7% for selenium concentrations of 7.3–0.6 ppm in copper and 1.6—3.1% for tellurium concentrations of 4.6—0.5 ppm.     

Some observations on the interferences in flameless atomic-absorption spectrometry of magnesium

Interferences in flameless atomic-absorption spectrometry of magnesium were investigated by the use of a molybdenum micro-tube atomizer with a double indentation. Two atomization processes were compared in order to understand the interference mechanism: atomization from separate indentations, and mixture-atomization. Most elements tested gave no interference in atomization from separate indentations, whereas magnesium absorption was somewhat reduced in mixture-atomization. However, zinc and lead caused broadened absorption profiles in mixture-atomization. Chromium interfered in both atomization processes. The origin of these interferences is discussed.     

Simultaneous determination of arsenic, selenium and mercury in foodstuffs by chemical vapour generation inductively coupled plasma optical emission spectroscopy

A procedure for the simultaneous determination of arsenic, selenium and mercury in foodstuffs has been developed. After a two-step microwave-assisted wet digestion in closed vessels, using concentrated nitric acid and hydrogen peroxide, the solution was analysed by inductively coupled plasma multichannel-based emission spectrometry using chemical vapour generation as the sample introduction system. All steps of the procedure, such as solid sample dissolution, pre-reduction to the suitable oxidation state, vapor generation, transport and atomization have been designed and optimised taking into account the concomitant presence of all the analytes considered. Temporal variation of analytical signals as well as interfering effects due to transition elements were also studied. Under the optimised operating conditions, the achieved detection limits for the simultaneous determination of arsenic, selenium and mercury in foodstuffs were 0.006, 0.023 and 0.018 microg g(-1), respectively, allowing their determination in real samples. Precision of the analytical procedure was 6.8% for arsenic, 5.2% for selenium and 7.7% for mercury (n=7). The accuracy and reliability of the method was verified by the analysis of both standard reference materials (rice flour and spinach leaves) and real samples (natural and Se-enriched rice).