Speciation neutron activation analysis

The chemical speciation study of trace elements in life sciences has been paid more and more attention in recent years, mainly because it can provide more significant information on the pathway, distribution, accumulation, excretion, and functions of trace elements in biological systems of interest than the traditional bulk composition study. Almost all speciation techniques consist of two steps. The first step involves the separation of species from the sample followed by the second step of element specific detection. The so-called molecular neutron activation analysis (MoNAA) or speciation neutron activation analysis (SNAA) is, in fact, a combination of conventional NAA with physical, chemical, or biological separation procedures in order to meet the ever-increasing need for chemical species study. 

Species distribution studies have shown that trace element (e.g. metals) concentrations in soils and sediments vary with physical location (e.g. depth below bed surface) and with particle size. In these speciation studies the total element content of each fraction was determined using a suitable trace element procedure, for example, solid sample analysis by X-ray emission spectroscopy or neutron activation analysis, or alternatively by dissolution of sample and analysis by ICPOES, AAS or ASV. The type of sample fraction analysed can vary, and a few... 

Table 2.4 Element speciation by analysis of different physical fractions of a soil or sediment using a sensitive analytical technique such as AAS or neutron activation analysis...

Techniques can be classified into two main categories those that detect total metal concentrations and those that detect some operationally defined fraction of the total. Methods which detect total concentrations such as inductively coupled plasma spectrometry, neutron activation analysis, atomic absorption spectrometry and atomic emission spectrometry have no inherent speciation capabilities and must be combined with some other separation technique(s) to allow different species to be detected (approach A in Fig. 8.2). Such separation methods normally fractionate a sample on the basis of size, e.g. filtration/ultrafiltration, gel filtration, or a combination of size and charge, e.g. dialysis, ion exchange and solvent extraction (De Vitre et al., 1987 Badey, 1989b Berggren, 1989 1990 Buffle et al., 1992). In all instances the complexes studied must be relatively inert so that their concentrations are not appreciably modified during the fractionation procedure. 

V. E. Negretti de Bratter, S. Recknagel, D. Gawlik, Speciation of Se, Fe and Zn in human milk whey the use of instrumental neutron activation analysis (INAA) to corroborate element profiles measured with inductively coupled plasma atomic emission spectrometry (ICP-AES), Fresenius J. Anal. Chem., 353 (1995), 137-142. 

Detection techniques of high sensitivity, selectivity, and ease of coupling with sample preparation procedures are of special interest for measuring PGM content in biological and environmental samples. ICP MS, electrothermal atomic absorption spectrometry (ET AAS), adsorptive voltammetry (AV), and neutron activation analysis (NAA) have fotmd the widest applications, both for direct determination of the total metal content in the examined samples and for coupling with instrumental separation techniques. Mass spectrometry coupled with techniques such as electrospray ionization (ESI) and capillary electrophoresis (CE) (e.g., ESI MS", LC ESI MS", LC ICP MS, CE MS", and CE ICP MS) offer powerful potential for speciation analysis of metals. MS is widely used for examination of the distribution of the metals in various materials (elemental analysis) and for elucidation of the... 

Speciation of organometallic compounds containing Au and Ag, on the other hand, was paid only scant attention as a subject for analytical research. The analytical methods that supported research on these compounds had to be dug out from the experimental sections of articles dealing with diverse aspects of chemistry, physics, biochemistry, etc. A review appeared on some of the antiinflammatory drugs shown in Table 1, discussing determination of Au in body fluids and pharmaceutical preparations, and speciation of the compounds and their metabolites. The methods included varieties of atomic absorption spectroscopy (AAS), varieties of neutron activation analysis (NAA), inductively coupled plasma spectrometry combined with mass spectrometric detection (ICP-MS),... 

Earlier methods used to determine mercury in biological tissue and fluids were mainly colorimetric, using dithizone as the com-plexing agent. However, during the past two to three decades, AAS methods - predominantly the cold vapor principle with atomic absorption or atomic fluorescence detection - have become widely used due to their simplicity, sensitivity, and relatively low price. Neutron activation analysis (NAA), either in the instrumental or radiochemical mode, is still frequently used where nuclear reactors are available. Inductively coupled plasma mass spectrometry (ICP-MS) has become a valuable tool in mercury speciation. Gas and liquid chromatography, coupled with various detectors have also gained much importance for separa-tion/detection of mercury compounds (Table 17.1). 

Keywords Trace elements Radionuclides Environment Water Soil Aerosol Plant Neutron activation analysis Atomic absorption spectrometry Inductively coupled plasma-atomic emission spectroscopy Inductively coupled plasma-mass spectrometry X-ray fluorescence Electrochemical methods Speciation... 

In addition, chromatographic separation combined with detection methods, such as neutron activation analysis (NAA) and ICP-MS, was also reported for chemical speciation analysis of iodine in water (Hou et at, 1999b Reifenhauser and Heumann, 1990 Schwehr and Santschi, 2003). In... 

Nuclear activation methods can provide high sensitivities for many but not all elements. These methods are capable of simultaneous multielement analysis and in some cases they may be essentially nondestructive analytical methods. One of the main disadvantages is the lack of information on chemical form (speciation) of the elements in the analyte. Neutron activation analysis is the most common form of activation analysis, but charged particle and photon activation analysis methods are also applied. 

Surface and bottom seawater samples from three locations in the Kattegat and Baltic Sea were analyzed for and in both iodide and iodate species, and total inorganic iodine by neutron activation analysis using nuclear reactions of l(n,y) I and I(n,y) I (Hou et al. 2001). Levels of 2.3 x 10 mol/1 for and 7 x 10 mol/1 for are obtained. Therefore, these isotopes of iodine are promising tracers of physical and biochemical process in the ocean, and research about the chemical speciation of and in ocean will be developed. ... 

Several methods are available for the determination of total aluminum in biological and other materials. Chemical and physicochemical methods are in most practical situations insensitive and inaccurate X-ray fluorescence is specific but lacks sensitivity neutron activation analysis is complex and subject to interferences, although it is a very sensitive technique. Nuclear magnetic resonance spectroscopy is not very sensitive but useful to get information on speciation [33]. Graphite furnace atomic absorption spectrometry (GFAAS) is the most widely used technique and can produce reliable results, provided that the matrix effects are recognized and corrected. Savory and Wills [19] reviewed chemical and physicochemical methods for the determination of aluminum in biological materials, e.g. X-ray fluorescence, neutron activation analysis, atomic emission spectrometry, flame emission, inductively coupled plasma emission spectroscopy, and AAS. 

Tungsten is principally found in the form of WO ions in biological media. Neutron activation analysis (NAA) is the most commonly used technique for its total determination ( W half-life 24 hr). Other methods such as atomic absorption spectrometry (AAS) or energy-dispersive X-ray fluorescence (EDXRF) are used more rarely. Moreover, no result about W speciation has been reported. 

In 1980s, Rack and colleagues at University of Nebraska carried out a series study on speciation of iodine, chlorinated pesticides, and seleium in urine using liquid chromatography and molecular neutron activation analysis. They developed procedures for trace level determination of iodoamino acids and... 

The information on the chemical speciation of trace elements in biological systems is much needed to evaluate their biological significance. Although a number of analytical techniques based on atomic behavior are available for the analysis of chemical speciation of trace elements, neutron activation analysis, as a nuclear analytical technique, can be successfully used in chemical speciation studies, after appropriate fractionation steps. Table 2.5 lists some typical applications of NAA in chemical speciation analysis of metalloproteins. The main advantages of NAA are of its high sensitivity and the absence of matrix effects inherited from the conventional neutron activation analysis. It can, therefore, be used to analyze the chemical species of trace elements in very small samples or complicated matrices, which is often impossible for non-nuclear techniques. 

The application of analytical methods to speciation measurements in complicated systems has remained rather limited, despite the considerable technological progress during the past 25 years. The characterisation methods (e.g. spectroscopy, nuclear magnetic resonance) are often limited to the study of isolated compounds at relatively high concentrations. They, therefore, necessitate the prior employment of sophisticated separation and pre-concentration methods which introduce severe risks of perturbation. The trace analysis methods are often insensitive to the chemical form of the elements measured (e.g. atomic absorption, neutron activation). Those which possess sufficient element specificity (e.g. electron spin resonance, fluorescence, voltammetry) still require significant development before their full potential can be realised. 

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