Thermal stabilization of inorganic and organo-selenium compounds for direct electrothermal atomic absorption spectrometry

A ⁷⁵Se tracer technique is used to show that Sb, Cd, Mn, Mo, Ni, KI, KIO3, Ag, Th, Tl, Zn and Zr quantitatively stabilize inorganic selenium. Only Mo, Ni and Ag were effective for organoselenium compounds in urine, and only molybdenum was partially successful for blood samples.     

Determination of tellurium in indium antimonide semiconductor material by electrothermal atomic absorption spectrometry

A method for the determination of the dopant concentration of tellurium in dissolved indium antimonide semiconductor material by electrothermal atomic absorption spectrometry (ETAAS) was developed. Efforts were made to investigate the optimal conditions of the furnace heating program and the effect of palladium modifier on the variation of tellurium and the background absorbance. According to the results obtained, the presence of palladium chemical modifier in the analysis of indium antimonide allowed the successful retention of tellurium in the graphite tube, and the optimum mass of palladium modifier was found to be dependent on the sample matrix concentration. The absorbance profile of tellurium and the background level were significantly improved when a pyrolysis temperature of 1100 degrees C and an atomization temperature of 2200 degrees C were employed in the optimized heating program. With the use of this method, a detection limit of 0.8 microg g(-1) tellurium in indium antimonide could be achieved. The applicability of the proposed method was evaluated by comparison with two independent methods, i.e. slurry sampling-ETAAS and ICP-MS. From the good agreement between the results, it was demonstrated that the proposed method is suitable for the determination of typical dopant concentrations of tellurium in indium antimonide.     

Glassy carbon tubes for electrothermal atomic absorption spectrometry

Summary The use of glassy carbon as a tube material in electrothermal atomic absorption spectrometry requires modifications to the power supply if temperatures and heating rates comparable to those for graphite tubes are to be obtained. Glassy carbon tubes frequently have a longer lifetime than pyrolytic graphite coated tubes made of polycrystalline electrographite. Peak height sensitivity for glassy carbon is better by a factor of two for some volatile elements, but up to a factor of five inferior for less volatile elements than that for pyrolytic graphite coated tubes. Peak area sensitivity is generally inferior by about a factor of two. Sample volume is limited to 5–10 l because of the smooth surface.From the signal shape it can be deduced that adsorption of analyte atoms at the tube wall plays an important role in glassy carbon, and is responsible at least in part for the lower sensitivity. Non-spectral interferences can be less pronounced in glassy carbon tubes for those interferents which interact with graphite tube surfaces. Glassy carbon is, however, no alternative to pyrolytic graphite coated tubes.

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Glasartiger Kohlenstoff als Rohrmaterial für elektrothermische Atomabsorptionsspektrometrie

     

Tube-probe atomisation in electrothermal atomic absorption spectrometry

A method is described in which liquid samples are deposited by a conventional autosampler on to a tubular graphite probe positioned inside a 7.5 mm i.d. Pye Unicam SP-9 atomiser cuvette. The tube-probe has certain advantages in comparison with the flat probe systems described previously. In particular, the precision of determinations in acid media is improved since the sample solution is better confined within the atomiser and hence the effects of droplet spreading are curtailed. Also, the tube-probe is shown to reduce diffusional loss effects at high atomiser temperatures, in comparison with flat probe operation. The characteristic mass values obtained for volatile and medium volatile elements are similar for tube and flat probes. Since a greater sample volume (up to 40 μl) can be deposited and dried in the tube-probe, improved detection limits are anticipated for these elements. For more involatile elements, the greater mass of the tube-probe results in poorer sensitivity by a factor of × 3 for V and × 4 for Cr.     

Flow injection on-line electrothermal atomic absorption spectrometry

Today the greatest hindrances to couple the continuous FI system to discrete ETAAS operations have been overcome as demonstrated by the great number of papers published in the last few years. This paper reviews 109 references to the development and expansion of the FI-ETAAS methodology. The selected FI-ETAAS systems, namely: on-line column preconcentration and separation systems; on-line knotted reactor preconcentration systems; on-line aerosol deposition systems; flow-injection for in situ trapping of volatile compounds and miscellaneous on-line systems.     

High current power supply for electrothermal atomic absorption spectrometry

A new power supply for electrothermal atomization — atomic absorption spectrometry (ETA-AAS) with associated equipment for temperature control is presented. The system is composed of two high current commercial batteries and a MOSFET switch which controls the temperature of the atomizer by switching the current in an on-off way through a feedback loop connected to a personal computer and suitably programmed peripherals. The delivered power can be changed from 0 to 100% in 1% steps which gives the possibility of roughly controlling both the temperature at low power when the temperature sensor is not working and the heating rate. With this system, curves for which the simultaneous presence of all atoms injected in the atomizer is claimed, have been extended to Pb, Ag, Tl and Zn. With a more conventional power supply previously used, such a claim could be made only for Cd and Hg.     

Recent developments in atomizers for electrothermal atomic absorption spectrometry

This review first describes general requirements to be met for suitable base materials used to produce electrothermal atomizers (ETAs). In this connection the physical and chemical properties of adequate types of graphite and metals are discussed. Further, various atomizer designs, their temperature dynamics during atomization and general performance characteristics are critically reviewed. For end-heated Massmann-type atomizers, discussions are focused on recent developments of, e.g., contoured tubes to achieve improved temperature homogeneity over the tube length, second surface atomizers to realize temporally isothermal atomization and tubes with graphite filters to reduce interference effects. The state-of-the-art of platform equipped, side-heated atomizers with integrated contacting bridges are characterized mainly with respect to heating dynamics, as well as susceptibility to interference- and memory effects. In contrast to end-heated ETAs, the tube ends of side-heated ETAs are freely located in the furnace compartment and, as a consequence of this configuration, convective gas flows can easily appear. The magnitude and effect of these flows on analytical performance are discussed and measures are suggested, permitting operation under diffusion controlled conditions. A critical comparison of classical constant temperature atomizers with state-of-the-art platform equipped ETAs is made and from this it is concluded that future ETA developments are likely to involve only minor modifications aiming at, e.g., the reduction of cycling times or the improvement of tube surface properties.     

Transverse heated filter atomizer for electrothermal atomic absorption spectrometry

The filter furnace atomization concept was applied for the transverse heated atomizer. A graphite filter with graphite fiber reeled onto it was inserted into the tube of the standard transverse heated graphite atomizer (THGA) in the place of the platform. Automatic plugging of the sampling hole was applied during the atomization stage. The performance of the filter atomizer (THFA), compared with the THGA, was tested for the determination of Ag, As, Au, Bi, Cd, Cu, Ga, In, Mn, Pb, Sb, Se and Tl. The analytical performances of the THFA displayed some advantages in comparison with the THGA. The sampling volume varied in the range of 5–90 μl, while drying time for any volume was less than half of that used for the THGA. Owing to the reduced diameter of the analytical zone (2 mm) along the filter axis, a sensitivity improvement was observed for all elements, 1.3–2.8-fold without plugging and 4.3–4.8-fold for Bi, Cd, Pb and Tl with plugging of the dosing hole. An increased peak width (by two to five times for the elements tested) limited the determination of less-volatile metals. The intensity of light decreased by 20–30% in comparison with the THGA. Taking into account the sensitivity, sampling volume, light loss and signal width, the calculated gain in relative detection limit is substantial (about 2.5–7 times) only for volatile elements when the plugging is applied. The pyrolysis temperatures for Ag, As, Au, Cd, Cu and Se in the THFA without addition of modifier were by 200–600°C higher than in the THGA using Pd/Mg modifier. The lifetime of THFA tubes was similar to that of THGA tubes.     

Recent developments in atomizers for electrothermal atomic absorption spectrometry

This review first describes general requirements to be met for suitable base materials used to produce electrothermal atomizers (ETAs). In this connection the physical and chemical properties of adequate types of graphite and metals are discussed. Further, various atomizer designs, their temperature dynamics during atomization and general performance characteristics are critically reviewed. For end-heated Massmann-type atomizers, discussions are focused on recent developments of, e.g., contoured tubes to achieve improved temperature homogeneity over the tube length, second surface atomizers to realize temporally isothermal atomization and tubes with graphite filters to reduce interference effects. The state-of-the-art of platform equipped, side-heated atomizers with integrated contacting bridges are characterized mainly with respect to heating dynamics, as well as susceptibility to interference- and memory effects. In contrast to end-heated ETAs, the tube ends of side-heated ETAs are freely located in the furnace compartment and, as a consequence of this configuration, convective gas flows can easily appear. The magnitude and effect of these flows on analytical performance are discussed and measures are suggested, permitting operation under diffusion controlled conditions. A critical comparison of classical constant temperature atomizers with state-of-the-art platform equipped ETAs is made and from this it is concluded that future ETA developments are likely to involve only minor modifications aiming at, e.g., the reduction of cycling times or the improvement of tube surface properties.     

Plasma afterglow atomization in electrothermal atomic absorption spectrometry

Potentialities of an Ar/H₂ microwave induced plasma afterglow at 8.2 mbar as an atomization source in electrothermal atomic absorption spectrometry have been examined. More specifically the atomization efficiency, as shown from appearance temperatures, and the reaction mechanisms of the atomization of the oxides and chlorides of alkaline earth and transition metals have been investigated and compared with conventional electrothermal atomization. For all the investigated metal chlorides and alkaline earth oxides, a considerable decrease in appearance temperature (some 500 K), is observed in the plasma afterglow. Such enhanced atomization is believed to be linked to reactions with H atoms. No plasma enhancement, however, is measured for the atomization of the transition metal oxides. All metal oxides are effectively reduced to free metal in the solid state by the Ar/H₂ afterglow, and as a consequence the supply rate is governed by the metal sublimation for these compounds. For metal chlorides, however, strong evidence is found for the atomization process to proceed via gas phase reactions.     

Effect of nitric acid for equal stabilization and sensitivity of different selenium species in electrothermal atomic absorption spectrometry

Determination of selenium by electrothermal atomic absorption spectrometry (ETAAS) is complicated by the presence of different species of this analyte. The presence of different oxidation states (−II, IV and VI) may result in different sensitivities obtained for each species rendering impossible the use of a single species for calibration. These species also exhibit different behaviours regarding thermal stabilities; the temperature program must be provided to conform to this problem. Chemical modifiers are commonly used for thermal stabilization of selenium species. In this study, experiments were carried out to demonstrate the effect of nitric acid in the presence of chemical modifiers. Nickel and palladium + magnesium were selected as the most commonly used chemical modifiers. Using both aqueous and human serum solutions it has been demonstrated that although chemical modifiers provide thermal stabilization of species so that higher ashing temperatures can be used, equal sensitivities cannot be achieved unless nitric acid is also present. Selenite, selenate, selenomethionine and selenocystine were used in experiments. When equal sensitivities for all these species are achieved, determination of total selenium by ETAAS can be performed by using a single species as the standard; selenite was used in this study. Precision was 5.0% or better using peak height signals. There was no significant difference in detection limits (3s) when Ni or Pd + Mg(NO₃)₂ was used as chemical modifier; 37 and 35 pg of selenium were found to be the detection limits for Ni and Pd + Mg(NO₃)₂ chemical modifiers, respectively. For chemical modifications, either 5 μg of Ni or 0.5 μg of Pd and 5 μg of Mg(NO₃)₂ were used; final solutions contained 2.5% HNO₃. In serum analyses, 10 μg of Ni was used in presence of 2.5% HNO₃.     

The tube-in-tube technique in electrothermal atomic absorption spectrometry

Summary A new tube-in-tube is presented. It consists of a small graphite tube which is inserted into a usual Perkin-Elmer graphite oven. Three bars, 1×1 mm over the whole length of the tube, prevent direct contact with the outer one and smoothe the temperature profile within the tube. It causes a thermal delay in the atomization of the atomic cloud. Thus, expulsion of the atomic cloud by the thermally expanding inert gas grows less important compared to its growth. A significant increase of sensitivity is the result.

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Die Rohr-in-Rohr-Technik bei der elektrothermalen Atomabsorptions-SpektrometrieII. Das Dreisteg-Rohr

Zusammenfassung Ein neuer Rohr-in-Rohr-Atomisator wird vorgestellt. Er besteht aus einem kleinen Graphitrohr, welches in ein übliches Perkin-Elmer-Graphitrohr hineingebracht wird. Drei Stege (1×1 mm) über die gesamte Rohrlänge verhindern den direkten Kontakt mit dem Außenrohr und glätten das Temperaturprofil im Innenrohr. Die Atomisierung erfolgt thermisch verzögert. Deshalb verliert das Austreiben der Atomwolke durch das sich thermisch ausdehnende Intergas im Verhältnis zu deren Anwachsen an Bedeutung. Ein deutlicher Anstieg der Meßempfindlichkeit ist das Ergebnis.

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Herrn Prof. Dr. W. Fresenius zum 70. Geburtstag gewidmet

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Part I: Atomspektrometrische Spurenanalytik, Bd. 2 (B. Welz, Ed.). Verlag Chemie Weinheim — in print     

Improved cesium sensitivity in electrothermal atomic absorption spectrometry

The sensitivity for cesium determination by electrothermal atomic absorption spectrometry is improved four-fold by the addition of a large excess of potassium nitrate. Zeeman background corrections is used to compensate for the large non-specific absorption signal resulting from the potassium. The characteristic concentration and detection limit are 0.44 and 2 μg l^?1, respectively, and the coefficient of variation is 2% at the 50 μg l^?1 level. The procedure is suitable for the rapid determination of cesium in leach solutions from nuclear waste fixation experiments.     

Time resolution of interferences in electrothermal atomic absorption spectrometry

A fast detector-amplifier-readout system is used for studying interferences in electrothermal graphite atomizers. The effects of different matrix components (K, B, Ca, Mg, and Cl), and graphite tube surfaces significantly alter the atomization processes of lead.     

电热原子吸收光谱法中原子形成过程的探讨

本文提出了测定电热原子吸收光谱法中原子形成过程动学参数的新方法, 并用此法测定了铜、铁、铝、钴和钼等原子形成过和的动力学级数和原子化能。结果表明这些元素的原子形成均为零动力学。通过比较原子化能的实验值与有关过程的焓变探讨了这些元素的原子化过程 。     

Utilization of electrodeposition for electrothermal atomic absorption spectrometry determination of gold

Gold was determined by electrothermal atomic absorption spectrometry after electrochemical preconcentration on the graphite ridge probe used as a working electrode and sample support. The probe surface was electrochemically modified with Pd, Re and the mixture of both. The electrolysis of gold was performed under galvanostatic control at 0.5 mA. Maximum pyrolysis temperature for the probe surface modified with Pd was 1200 °C, with Re 1300 °C. The relative standard deviation for the determination of 2 μg l^− 1 Au was not higher than 5.6% (n = 8) for 2 min electrodeposition. The sensitivity of gold determination was reproducible for 300 electrodeposition and atomization cycles. When the probe surface was modified with a mixture of Pd and Re the detection limit was 31 ng l^− 1 for 2 min electrodeposition, 3.7 ng l^− 1 for 30 min, 1.5 ng l^− 1 for 1 h and 0.4 ng l^− 1 for 4 h electrodeposition, respectively. The procedure was applied to the determination of gold in river water samples. The relative standard deviation for the determination of 2.5 ng l^− 1 Au at 4 h electrodeposition time at 0.5 mA was 7.5%.     

Atomic absorption spectrometry of tellurium with electrothermal atomization in a molybdenum microtube

Hydrogen, added to argon purge gas, is necessary to protect the molybdenum microtube atomizer from oxidation, but it increases the atomization temperature and decreases the maximum absorbance of tellurium. A mixture of thiourea and copper removes the interfering effects of diverse elements and counteracts the effect of hydrogen. Tellurium (20–200 ppm) in copper can be determined after extraction as a chloride complex.