Absorption electrothermal atomic

The use of furnaces as atomizers for quantitative AAS goes back to the work of Lvov and led to the breakthrough of atomic absorption spectrometry towards very low absolute detection hmits. In electrothermal AAS graphite or metallic tube or cup furnaces are used, and through resistive heating temperatures are achieved at which samples can be completely atomized. For volatile elements this can be accomplished at temperatures of 1000 K whereas for more refractory elements the temperatures should be up to 3000 K. 

The high absolute power of detection of electrothermal AAS is due to the fact that the sample is completely atomized and brought in the vapor phase as well as to the fact that the free atoms are kept in the atom reservoir for a long time. The signals obtained are transient, as discussed earlier. 

Apart from graphite tube furnaces, both cups and filaments are used as atomizers in electrothermal AAS [271). The models originally proposed by L vov et al. [171] and by Massmann [172] were described in Section 3.4. In the case of the latter, which is most widely used, the optical beam is led centrally through the graphite tube, which is closed at both ends with quartz viewing ports mounted in the cooled tube holders. Sample ahquots are introduced with the aid of a micropipette or a computer controlled dispenser through a sampling hole in the middle of the tube. 

Normal graphite furnaces have a temperature profile and thus differences in the spreading of the analyte over the graphite surface may lead to changes in the volatilization behavior from one sample to another. This effect can be avoided by using a transversally-heated furnace, where the temperature is constant over the whole tube length (Fig. 84). The latter furnace, which has been proposed by Freeh et al. 

As discussed earlier, tungsten furnaces, as first proposed by Sychra et al. [175a], are useful for the determination of refractory carbide forming elements, which in the case of a graphite furnace may suffer from poor volatilization, but they are more 

Despite the progress made in graphite furnace AAS, the basic mechanisms have not been fully established as yet. This applies to the processes responsible for the atomization itself as well as for the transfer of free atoms to the absorption volume and their removal from this volume. The time-dependence of the atom population in the absorption volume can be described by  

In hot flames, such as the carbon-rich flame, the equilibrium would lie on the right side. However, in the presence of an excess of oxyanions (O-X) the equilibrium is shifted to the left and no free M atoms are formed. This can be corrected for by adding a metal (R) that forms even more stable oxysalts and releases the metal M again. To this end. La and Sr compounds can be used according to  

When LaCla is added to the sample solutions, the phosphate can be bound as LaP04. 

With alkali metal elements, the free atom concentrations in the flame can decrease as a result of ionization, which occurs particularly in hot flames. This leads to a decrease of the absorbances for these elements. However, it also may lead to false analysis results, as the ionization equilibrium for the analyte element is changed by changes in the concentration of the easily ionized elements. In order to suppress these effects, ionization buffers can be added. The addition of an excess of Cs because of its low ionization potential is most effective for suppressing changes in the ionization of other elements, as it provides for a high electron number density in the flame. 

Physical interferences may arise from incomplete volatilization and occur especially in the case of strongly reducing flames. In steel analysis, the depression of the Cr and Mo signals as a result of an excess of Fe is well known. It can be reduced by adding NH4CI. Further interferences are related to nebulization effects and arise from the influence of the concentration of acids and salts on the viscosity, the density, and the surface tension of the analyte solutions. Changes in physical properties from one sample solution to another influence the aerosol formation efficiencies and the aerosol droplet size distribution, as discussed earlier. However, related changes of the nebulizer gas flows also influence the residence time of the particles in the flame. 

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Element Wavelength, nm Flame emission Flame atomic absorption Electrothermal atomic absorption Argon ICP Plasma atomic fluorescence... 

The section on Spectroscopy has been retained but with some revisions and expansion. The section includes ultraviolet-visible spectroscopy, fluorescence, infrared and Raman spectroscopy, and X-ray spectrometry. Detection limits are listed for the elements when using flame emission, flame atomic absorption, electrothermal atomic absorption, argon induction coupled plasma, and flame atomic fluorescence. Nuclear magnetic resonance embraces tables for the nuclear properties of the elements, proton chemical shifts and coupling constants, and similar material for carbon-13, boron-11, nitrogen-15, fluorine-19, silicon-19, and phosphoms-31. 

Miscellaneous. Trace analyses have been performed for a variety of other materials. Table 9 Hsts some uses of electrothermal atomic absorption spectrometry (etaas) for determination of trace amounts of elements in a variety of matrices. The appHcations of icp /ms to geological and biological materials include the following (165) ... 

INDIRECT DETERMINATION OF ASCORBIC ACID BY ELECTROTHERMAL ATOMIC ABSORPTION SPECTROMETRY... 

COMPARISON OF MICROWAVE ASSISTED EXTRACTION METHODS FOR THE DETERMINATION OF PLATINUM GROUP ELEMENTS IN SOIL SAMPLES BY ELECTROTHERMAL ATOMIC ABSORPTION SPECTROMETRY AFTER PHASE SEPARATION-EXTRACTION... 

The development of methods using sorbents modified with analytical reagents that enable analytical signal measuring directly on the surface by solid-phase spectrometry, visually or by electrothermic atomic absorption spectroscopy (ETAAS) after elution is now a subject of growing interest. 

ACTING MECHANISM OF INORGANIC CHEMICALS MODIFIERS IN ELECTROTHERMAL ATOMIC ABSORPTION... 

Lead in soil slurries Electrothermal atomic absorption spectrometry... 

Electrothermal Atomic Absorption Spectrometry of Trace Metals in Biological Fluids... 

The scope of this review Is limited to electrothermal atomic absorption spectrometry, with emphasis upon Its clinical applications. This article Is Intended to supplement the recent treatises on the basic technique which have been written by Aggett and Sprott ( ) > Ingle ( ), Klrkbrlght (34), Price (63), and Woodrlff (83). This resume does not consider various related topics, such as (a) atomic fluorescence or emission spectrometry (b) non-flame atomization devices which employ direct current... 

Inadequate regulation of atomizer temperature Is a major source of Imprecision In electrothermal atomic absorption spectrometry. The programmed heating of electrothermal atomizers can be achieved by five different methods, depending upon the electrical or physical parameters which are monltorled during... 

Micro-pipetting instruments such as the "Eppendorf or "Oxford pipettors with disposable plastic cone tips are customarily employed to dispense the liquid samples into electrothermal atomizers. Sampling problems which are associated with the use of these pipettors are among the troublesome aspects of electrothermal atomic absorption spectrometry (67,75). The plastic cone-tips are frequently contaminated with metals, and they should invariably be cleaned before use by soaking in dilute "ultra pure nitric acid, followed by multiple rinses with demineralized water which has been distilled in a quartz still. 

Aqueous standard solutions are a source of certain difficulties In electrothermal atomic absorption spectrometry of trace metals In biological fluids The viscosities and surface tensions of aqueous standard solutions are substantially less than the viscosities and surface tensions of serum, blood and other proteln-contalnlng fluids These factors Introduce volumetric disparities In pipetting of standard solutions and body fluids, and also cause differences In penetration of these liquids Into porous graphite tubes or rods Preliminary treatment of porous graphite with xylene may help to minimize the differences of liquid penetration (53,67) A more satisfactory solution of this problem Is preparation of standards In aqueous solutions of metal-free dextran (50-60 g/llter), as first proposed by Pekarek et al ( ) for the standardization of serum chromium analyses This practice has been used successfully by the present author for standardization of analyses of serum nickel The standard solutions which are prepared In aqueous dextran resemble serum In regard to viscosity and surface tension Introduction of dextran-contalnlng standard solutions Is an Important contribution to electrothermal atomic absorption analysis of trace metals In body fluids. 

N1 and Zn from a graphite rod were significantly lower than from a tantalum filament, suggesting that these free metal atoms can be liberated by chemical reduction of their respective oxides, rather than by direct thermal dissociation. Findlay et al (19) emphasized the hazards of preatomlzatlon losses of trace met s In electrothermal atomic absorption spectrometry, when the ashing temperature Is permitted to exceed the minimum temperature for vaporization of the analyte. 

In Table I are listed comprehensive citations of published methods for analyses of trace metals In body fluids and other clinical specimens by means of electrothermal atomic absorption spectrometry. Readers are cautioned that many of the early methods that are cited In Table I have become outmoded, owing to Improvements In Instrumentation for electrothermal atomic absorption spectrometry. All of the published methods need to be critically evaluated In the prospective analyst s laboratory before they can be confidently employed for diagnostic measurements of trace metals In body fluids. Despite these caveats, the author believes that Table I should be helpful as a guide to the growing literature on clinical and biological applications of electrothermal atomic absorption spectrometry. 

Inductively coupled plasma atomic emission spectrometry Electrothermal atomic absorption spectrometry High pressure liquid chromatography... 

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