Atomic absorption with electrothermal atomisation

Graphite Furnace Atomic Absorption Spectrometry (GFAAS) or Atomic Absorption with Electrothermal Atomisation (ETAAS)... 

Olayinka, K.O., Haswell, S.J. and Grzeskowiak, R. (1989) Speciation of cadmium in crab-meat by reversed-phase high-performance liquid chromatography with electrothermal atomisation atomic absorptive spectrophotometric detection in a model gut digestive system. J. Anal. At. Spectrom., 4, 171-175. 

Elemental analysis of body tissues and fluids by atomic absorption spectrometry with electrothermal atomisation has advanced significantly the understanding of the role of trace elements in clinical biochemistry. All of those aspects of metabolic processes that are affected by changes in the concentrations of accessible trace elements have been studied. These include deficiencies of essential trace elements as a result of inherited or acquired metabolic disorders, or from nutritional inadequacy and excesses of trace elements producing toxicity states as a result of inherited metabolic disorders involving essential trace elements or from the inappropriate exposure to, or ingestion of, non-essential trace elements. 

Hodges, D. J., Skelding, D., Determination of Lead in Urine by Atomic-Absorption Spectroscopy with Electrothermal Atomisation, Analyst [London] 106 [1981] 299/304. 

Bruland et al. [122] have shown that seawater samples collected by a variety of clean sampling techniques yielded consistent results for copper, cadmium, zinc, and nickel, which implies that representative uncontaminated samples were obtained. A dithiocarbamate extraction method coupled with atomic absorption spectrometry and flameless graphite furnace electrothermal atomisation is described which is essentially 100% quantitative for each of the four metals studied, has lower blanks and detection Emits, and yields better precision than previously published techniques. A more precise and accurate determination of these metals in seawater at their natural ng/1 concentration levels is therefore possible. Samples analysed by this procedure and by concentration on Chelex 100 showed similar results for cadmium and zinc. Both copper and nickel appeared to be inefficiently removed from seawater by Chelex 100. Comparison of the organic extraction results with other pertinent investigations showed excellent agreement. 

Figure 1.7 Electrothermal atomisation atomic absorption spectrometry, (a) Photograph of a graphite tube, (b) Photograph of a L vov platform, (c) Schematic front and side-on views of a graphite tube with a L vov platform.

To avoid problems previously encountered with flame atomic absorption spectrometry of arsenic, and also with flameless methods such as that in which the dementis converted to arsine, Ohta and Suzuki [25] proposed an alternative method based on electrothermal ionisation with a metal microtube atomiser. Effective atomisation can be achieved by the addition of thiourea to the arsenic solution or by preliminary extraction of the arsenic-thionalide complex. The second method is recommended for soil samples so as to avoid interference due to the presence of trace elements. 

The determination of arsenic by atomic absorption spectrometry with thermal atomisation and with hydride generation using sodium borohydride has been described by Thompson and Thomerson [29], and it was evident that this method couldbe modified for the analysis of soil. Thompson and Thoresby [30] have described a method for the determination of arsenic in soil by hydride generation and atomic absorption spectrophotometry using electrothermal atomisation. Soils are decomposed by leaching with a mixture of nitric and sulfuric acids or fusion with pyrosulfate. The resultant acidic sample solution is made to react with sodium borohydride, and the liberated arsenic hydride is swept into an electrically heated tube mounted on the optical axis of a simple, lab oratory-constructed absorption apparatus. 

Flameless atomic absorption using an electrothermal atomiser is essentially a non-routine technique requiring specialist expertise. It is slower than flame analysis only 10—20 samples can be analysed in an hour furthermore, the precision is poorer (1—10%) than that for conventional flame atomic absorption (1%). The main advantage of the method, however, is its superior sensitivity for any metal the sensitivity is 100—1000 times greater when measured by the flameless as opposed to the flame technique. For this reason flameless atomic absorption is employed in the analysis of water samples where the flame techniques have insufficient sensitivity. An example of this is with the elements barium, beryllium, chromium, cobalt, copper, manganese, nickel and vanadium, all of which are required for public health reasons to be measured in raw and potable waters (section I.B). Because these elements are generally at the lOOjugl-1 level and less in water, their concentration is below the detection limit when determined by flame atomic absorption as a result, an electrothermal atomisation (ETA) technique is often employed for their determination. 

The disadvantages of electrothermal atomisation (ETA) — atomic absorption spectrometry (AAS) are the physical, chemical and spectral interferences, these being more severe than with flame atomic absorption spectrometry (FAAS), and which depend critically upon the experimental and operational conditions within the atomiser and the nature of the chemical pretreatment used. It is not intended to discuss here the theoretical aspects of these interferences which have been reviewed excellently elsewhere [2], but it is pertinent to consider briefly how these interferences affect the various stages of the analysis and how they may be minimised. 

Hydride generation atomic absorption spectrometry and electrothermal atomisation atomic absorption spectrometry may also be employed for the measurement of selenium in biological samples. A comparison was made (MacPherson et al., 1988) of these methods with the fluorimetric method described here and all three methods were found to give accurate, reproducible results when samples of plasma and urine with certified selenium contents were analysed. 

Control water hyacinths, grown under the same controlled hydroponic conditions, but without platinum added were irradiated under similar conditions. A large photopeak at 158 keV resulted, whereas the 208 keV peak was not visible. Thus some interfering nuclide with a photopeak around 158 keV is present even in the control material. The interfering elements are under further investigation. This interference seems to be present both in animal and in plant tissue. LeRoy (16) has compared the results of the analysis of canine heart, liver and muscle by both electrothermal atomisation atomic absorption spectroscopy (ETA AAS) and INAA. It was found that the results for Pt using INAA... 

Atomic absorption spectroscopy is now established as one of the most useful tools for analysing trace metals in samples which may be taken into solution. It has wide applicability, is inexpensive and can be used with confidence by a wide range of analysts. The rapid growth and advancement of electrothermal atomisation methods and their subsequent automation has consolidated the technique s position by extending the dynamic analytical range down to concentration levels that other techniques cannot reach. 

CONTENTS 1. Basic Principles (J. W. Robinson). 2. Instrumental Requirements and Optimisation (J. E. Cantle). 3. Practical Techniques (J. E. Cantle). 4a. Water and Effluents (B. J. Farey and L A. Nelson). 4b. Marine Analysis by AAS (H. Haraguchi and K. Fuwa). 4c. Analysis of Airborne Particles in the Workplace and Ambient Atmospheres (T.J. Kneip and M. T. Kleinman). 4d. Application of AAS to the Analysis of Foodstuffs (M. Ihnat). 4e. Applications of AAS in Ferrous Metallurgy (K. Ohis and D. Sommer). 4f. The Analysis of Non-ferrous Metals by AAS (F.J. Bano). 4g. Atomic Absorption Methods in Applied Geochemistry (M. Thompson and S. J. Wood). 4h. Applications of AAS in the Petroleum Industry W. C. Campbell). 4i. Methods forthe Analysis of Glasses and Ceramics by Atomic Spectroscopy (W. M. Wise et al.). 4j. Clinical Applications of Flame Techniques (B.E. Walker). 4k. Elemental Analysis of Body Fluids and Tissues by Electrothermal Atomisation and AAS (H. T. Delves). 4I. Forensic Science (U. Dale). 4m. Fine, Industrial and Other Chemicals. Subject Index. (All chapters begin with an Introduction and end with References.)... 

Apostoli, P., Alessio, L, Dal Farra, M. and Fabbri, P.L (1988). Determination of vanadium in urine by electrothermal atomisation atomic absorption spectrometry with graphite tube pre-heating, J. Anal. Atomic Spectr., 2, 471. 

The half width of elemental lines is of the order of 0.002 nm when observed by emission spectroscopy with flame or electrothermal atomisation. A number of reasons can cause broadening of the linewidth, of which the most important and best understood are natural, pressure, resonance, and Doppler broadening. If a stable and sensitive detection is to be achieved, the linewidth of the excitation radiation must be narrower than the full width at half maximum (FWHM) of the analyte line. Under these conditions, the entire radiant energy produced by the excitation source will be available for absorption by the analyte. The typical line sources used for atomic absorption are element specific excitation sources such as the hollow cathode lamp or the electrodeless discharge lamp. But even continuum sources can be used with appropriate instrumental designs. 

Electrothermal atomisation (graphite furnace) atomic absorption spectrophotometer with a device for correcting background absorption. 

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