Graphite furnace atomic absorption with other techniques

Many of the published methods for the determination of metals in seawater are concerned with the determination of a single element. Single-element methods are discussed firstly in Sects. 5.2-5.73. However, much of the published work is concerned not only with the determination of a single element but with the determination of groups of elements (Sect. 5.74). This is particularly so in the case of techniques such as graphite furnace atomic absorption spectrometry, Zeeman background-corrected atomic absorption spectrometry, and inductively coupled plasma spectrometry. This also applies to other techniques, such as voltammetry, polarography, neutron activation analysis, X-ray fluroescence spectroscopy, and isotope dilution techniques. 

One of the advantages of the isotope dilution technique is that the quantitative recovery of the analytes is not required. Since it is only their isotope ratios that are being measured, it is necessary only to recover sufficient analyte to make an adequate measurement. Therefore, when this technique is used in conjunction with graphite furnace atomic absorption spectrometry, it is possible to determine the efficiency of the preconcentration step. This is particularly important in the analysis of seawater, where the recovery is very difficult to determine by other techniques, since the concentration of the unrecovered analyte is so low. In using this technique, one must assume that isotopic equilibrium has been achieved with the analyte, regardless of the species in which it may exist. 

Other analytical tools have also been used as offline detectors for the FFF techniques. Bio et al. (1995) used for this purpose a graphite furnace atomic absorption spectrometer (GFAAS) to analyze colloidal kaolin particles. Contado et al. (1997) used same design to characterize river-suspended particulate matter of size <1 pm. However, the centrifuges available for SdFFF are only capable of separating particles with sizes down to 80 nm. Usage of SdFFF for characterization of HS is therefore restricted because of this limitation. 

In EMEP, ICP-MS is dehned as the reference technique. The exception is mercury, where cold vapor atomic fluorescence spectroscopy (CV-AFS) is chosen. Other techniques may be used, if they are shown to yield results of a quality equivalent to that obtainable with the recommended method. These other methods include graphite furnace atomic absorption spectroscopy (GF-AAS), flame-atomic absorption spectroscopy (F-AAS), and CV-AFS. The choice of technique depends on the detection limits desired. ICP-MS has the lowest detection limit for most elements and is therefore suitable for remote areas. The techniques described in this manual are presented with minimum detection limits. Table 17.2 lists the detection limits for the different methods. 

Inorganic extractables/leachables would include metals and other trace elements such as silica, sodium, potassium, aluminum, calcium, and zinc associated with glass packaging systems. Analytical techniques for the trace analysis of these elements are well established and include inductively coupled plasma—atomic emission spectroscopy (ICP-AES), ICP-MS, graphite furnace atomic absorption spectroscopy (GFAAS), electron microprobe, and X-ray fluorescence. Applications of these techniques have been reviewed by Jenke. " An example of an extractables study for certain glass containers is presented by Borchert et al. ". ... 

Among the common metal ions, only aluminum and cobalt gave peaks when complexed with 8-quinolinol and eluted with SDS-acetonitrile mobile phases. However, the peaks appeared very close to each other with spectrophotometric detection (Fig. 12.2). The selective determination of aluminum was only possible with fluorimetric detection. The addition of SDS as well as several other surfactants to the aluminum complex solution, increased the fluorescence intensity. The procedure did not require deproteinization prior to analysis. The most commonly used technique for aluminum in human serum is graphite-furnace atomic absorption spectrophotometry, which is often limited due to serum matrix interference. 

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. 

The relative advantages and disadvantages ofvoltammetric and atomic absorption methodologies are listed below. It is concluded that for laboratories concerned with aquatic chemistry of metals (which includes seawater analysis), instrumentation for both AAS (including potentialities for graphite furnace AAS as well as hydride and cold vapour techniques) and voltammetry should be available. This offers a much better basis for a problem-orientated application of both methods, and provides the important potentiality to compare the data obtained by one method with that obtained in an independent manner by the other, an approach that is now common for the establishment of accuracy in high-quality trace analysis. 

Different analytical techniques such as ICP-OES (optical emission spectrometry with inductively coupled plasma source), XRF (X-ray fluorescence analysis), AAS (atomic absorption spectrometry) with graphite furnace and flame GF-AAS and FAAS, NAA (neutron activation analysis) and others, are employed for the trace analysis of environmental samples. The main features of selected atomic spectrometric techniques (ICP-MS, ICP-OES and AAS) are summarized in Table 9.20.1 The detection ranges and LODs of selected analytical techniques for trace analysis on environmental samples are summarized in Figure 9.15.1... 

Metbylmercury, in turn, is decomposed abi-otically and by bacteria containing mercuric reductase and organomercurial lyase these demethylating strains of bacteria are common in the environment and have been isolated from water, sediments, soils, and the G1 tract of humans and other mammals. Other mechanisms can reduce inorganic Hg + to Hg in freshwater, with Hg production higher under anoxic conditions, in a chloride-free environment, and at pH 4.5. Metbylmercury concentrations in tissues of marine fishes can now be detected at levels >10.0p,g/kg tissue using graphite furnace sample preparation techniques and atomic absorption spectrometry. 

Other direct methods used more routinely for solid sampling analysis make use of an atomization cell, usually a graphite furnace, and optical spectrometry. Optical spectrometry techniques used are inductively coupled plasma (ICP) and atomic absorption spectrometry (AAS). This last technique, solid sampling atomic absorption spectrometry (SS-AAS), is used by far the most and thus will be dealt with more comprehensively. 

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