Improved sensitivity using a microcomputer for electrothermal atomic absorption spectrometry with a metal microtube

Data enhancement by signal accumulation, scale expansion after background subtraction, and smoothing with the aid of the microcomputer enables limits of detection to be improved by up to an order of magnitude. Data are reported for 15 elements.     

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.     

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.     

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.     

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     

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

     

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 。     

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.     

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.     

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.     

钨丝电热蒸发-氩/氢火焰原子吸收光谱分析方法

基于钨丝电热蒸发设备,建立了一种全新的钨丝电热蒸发-氩/氢火焰串联原子吸收光谱系统.研究了系统抗酸、抗盐能力,结果表明:Na<'+>和Ca<'2+>质量浓度小于400 mg/L、Mg<'2+>质量浓度小于1500 mg/L时不干扰测定.在优化的仪器条件下:Pb、Cd、Au和Ag的检出限分别为:0.016、0.0005、...     

Determination of selenium in water by electrothermal atomic absorption spectrometry

Summary The electrothermal atomization of selenium has been investigated for the accurate determination of selenium in water samples. Hydrogen seriously affects the atomization temperature of selenium in a molybdenum micro-tube atomizer. The atomization of selenium also suffers from serious interferences caused by salts and other elements. The extraction of selenium diethyldithiocarbamate complex serves to eliminate the interferences from the matrix. The addition of copper allows the suppression of interferences from elements extracted with selenium. The method permits the determination of selenium(IV) and selenium(VI) separately.This research was in part funded by the Ministry of Education, Science and Culture, Japan, under Grant-in-Aid for Scientific Research, for which we express our appreciation.     

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.     

Analysis of cobalt in plasma by electrothermal atomic absorption spectrometry

Summary A method for the determination of traces of cobalt in plasma is described. The sample is digested in a test tube using a mixture of nitric and perchloric acid. Ammonium-pyrrolidine dithiocarbamate is added as chelating agent, and after pH-adjustment to pH 9±0.1, cobalt is extracted into methyl-isobutyl ketone.Recovery studies using Co-60 showed that losses of cobalt during the procedure, including digestion and extraction are less than 3%. Possible contamination from the steel needle used is tested and discussed. The coefficient of variation for the method is 9.5% at the 0.20 g/l level. A realistic determination limit following this procedure is estimated to be 0.06 g/l. Using this method, the cobalt concentration in plasma from 32 control persons was determined to 0.15 ±0.07 g/l. For 10 refinery workers daily exposed to aerosols of CoCl₂ the determined average was 9.7±7.1 g/l.

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Analyse von Kobalt in Plasma mit Hilfe der elektrothermischen AAS

Zusammenfassung Bei dem beschriebenen Verfahren wird die Probe mit Hilfe von Salpetersäure/Perchlorsäure aufgeschlossen. Als Komplexierungs-Reagens wird Ammonium-pyrrolidindithiocarbamat zugefügt und nach pH-Einstellung auf 9±0,1 wird Co mit Methylisobutylketon extrahiert.Mit Hilfe von Co-60 wurde festgestellt, daß die durch Aufschluß und Extraktion verursachten Verluste weniger als 3% betragen. Eine mögliche Verunreinigung durch die benutzten Stahlnadeln wurde untersucht und diskutiert. Der Variationskoeffizient beträgt 9,5% bei 0,2 g Co/l. Die Bestimmungsgrenze nach diesem Verfahren liegt bei 0,06 g Co/l. Die Kobaltkonzentration im Plasma von 32 Kontrollpersonen wurde zu 0,15±0,07 g Co/l bestimmt. Für 10 Raffineriearbeiter, die täglich CoCl₂-Aerosolen ausgesetzt waren, wurde ein Durchschnitt von 9,7±7,1 g Co/l gefunden.

     

Determination of aluminium in silicon by electrothermal atomic absorption spectrometry

The sample is decomposed with hydrofluoric and nitric acids and the diluted solution is injected into the graphite furnace. For a 100-mg sample, the detection limit (3 σ) is 1.2 μg AI g^-1. The coefficient of variation is 3–13% for 9–7000 μg Al g^-1 in silicon.     

Determination of vanadium in urine by electrothermal atomic absorption spectrometry

After wet ashing of the urine sample with nitric acid, vanadium is chelated with cupferron, extracted into 4-methylpentan-2-one and determined by atomic absorption spectrometry with a pyrolytically-coated graphite furnace atomizer. The sensitivity allows the precise determination of 1–500 μg V l^-1 in urine. The coefficient of variation for triplicate urine measurements is <8% for 10 μg V l^-1.