Heavy element species, determination

In this paper, the application of a number of sensitive and precise methods for the determination of trace elements, heavy element species, and organic compounds in materials from one oil shale research retort process and from a solvent-refined coal pilot plant operation are discussed. The methods used were chosen both for their sensitivity and their relative freedom from interferences. 

Owing to their superior fluorescent yield, heavy elements ordinarily yield considerably more intense XRF bands than the light elements. This feature can be exploited to determine the concentration of inorganic species in a sample, or the concentration of a compound that contains a heavy element in some matrix. Many potential XRF applications have never been developed owing to the rise of atomic spectroscopic methods, particularly inductively coupled plasma atomic emission spectrometry [74]. Nevertheless, under the right set of circumstances, XRF analysis can be profitably employed. 

Due to the various health risks of different element species, there are a multitude of applications for natural water samples in this field (e.g., Cr and Sb speciation or Br and I determination).19 The investigation of heavy metal complexes with humic substances by isotope dilution SEC-ICP-MS has been described, for example, by McSheehy and Mester.20 Copper, zinc and molybdenum were found to form complexes with similar size fractions of humic substances in seepage water samples from soils. Sturgeon s group proposed the use of solid phase microextraction (SPME)... 

While significant uncertainty exists in determining the absolute stellar abundances of the heavy elements, the relative isotopic abundance of an atomic species can be determined somewhat independently of the atmospheric modelling uncertainties [4, 29]. Observations of different ZrO bands in a star do produce slightly different surface abundance values, but the uncertainty this introduces into our analysis of stellar nucleosynthesis is small compared to other uncertainties we have already discussed. In addition, the heavy element... 

Isotopic Studies. In this analysis mode the mass spectrometer Is used to determine the relative abundance of different Isotopes of the same element. SIMS Is the only common surface analysis technique that can distinguish the Isotopes of both the light and heavy elements. This mode Is advantageously used In mechanistic studies using Isotopically labelled samples. By using different Isotopes of the same element experiments can be performed without concern for the differences In chemical effects between the species. 

Vne of the common problems encountered in studies of aqueous geo-chemistry and water pollution is proper identification of a particular species of an element or compound that may be present in the system. The use of electron spin resonance (ESR) spectroscopy to determine the presence and concentration of equilibrium and/or nonequilibrium metal species in natural water systems has not been adequately investigated. Coincidentally, Mn2, one of the easiest elemental species to detect by ESR, is also one of the dissolved species of considerable concern in problems related to heavy metal pollution and aqueous geochemistry. Furthermore, with proper design there exists the possibility of using electron spin resonance as the basis of a remote monitoring system for the detection of appropriate heavy metals in natural water systems. 

While ranges of total concentration serve to set bounds for experimentally determining effects on marine populations, the actual species of metal ion available to the biological population is of importance. Sillen, in a classic paper, has computed the stable species of many metals in sea water21). He concluded, for example, that Hg+2, Cd+2, and Pb+2 exist primarily as chloride complexes. pH determines the availability of the hydroxide ion and thereby the solubility of metal hydroxides. Sillen assumed a pH of 8.1 0.2 as representative. Significant variations could occur, however, in estuarine waters. When concentrations of trace elements were compared with calculations of their solubility products and stability constants, the observed values were considerably less than the calculated values. The implication is that the heavy metals are not in equilibrium with solid phases of their salts, but that other processes, such as chelation and adsorption, control their concentration. 

Examples of applications of X-ray spectrometric analytical techniques to elemental determinations in a variety of materials are presented in Table 2.12. Some recent applications papers may be mentioned. Total reflection XRF has been applied by Xie et al. (1998) to the multielement analysis of Chinese tea (Camellia sinensis), and by Pet-tersson and Olsson (1998) to the trace element analysis of milligram amounts of plankton and periphyton. The review by Morita etal. (1998) on the determination of mercury species in environmental and biological samples includes XRF methods. Alvarez et al. (2000) determined heavy metals in rainwaters by APDC precipitation and energy dispersive X-ray fluorescence. Other papers report on the trace element content of colostrum milk in Brazil by XRF (da Costa etal. 2002) and on the micro-heterogeneity study of trace elements in uses, MPI-DING and NIST glass reference materials by means of synchrotron micro-XRF (Kempenaers etal. 2003). 

If the species and quantities of the components of the natural material before and after the calorimetric measurement are known sufficiently well, the calorific value Qp allows to determine an apparently standard enthalpy of formation at T = 298.15 K and p = 1 bar to be assigned to the natural material. Chemical analysis usually determines the fuel components (C, H, N, O, S) as elements, the ash components as oxides, and the heavy metals as elements. 

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