Multi-element compounds

Conventional XRF analysis uses calibration by regression, which is quite feasible for known matrices. Both single and multi-element standards are in use, prepared for example by vacuum evaporation of elements or compounds on a thin Mylar film. Comparing the X-ray intensities of the sample with those of a standard, allows quantitative analysis. Depending on the degree of similarity between sample and standard, a small or large correction for matrix effects is required. Calibration standards and samples must be carefully prepared standards must be checked frequently because of polymer degradation from continued exposure to X-rays. For trace-element determination, a standard very close in composition to the sample is required. This may be a certified reference material or a sample analysed by a primary technique (e.g. NAA). Standard reference material for rubber samples is not commercially available. Use can also be made of an internal standard,... 

Since 1960, it has been demonstrated by various analytical procedures that high concentrations of arsenic were present in Napoleon s hair.88 Multi-element analysis of two specimens of Napoleon s hair by ICP-MS after mineralization in concentrated nitric acid resulted in arsenic concentrations (42.1 and 37.4(xgg-1) about 40 times higher than normal values, confirming the hypothesis of a significant exposure to arsenic. However, mercury (3.3. and 4.7(xgg 1), antimony (2.1 and 1.8(xgg 1) and lead (229 and 112p,gg-1) were also detected at elevated levels. The elevated concentrations of Sb and Hg are in agreement with the data already known about the therapeutic treatments given to Napoleon (calomel and tartar emetic are compounds of mercury and antimony, respectively).88... 

Multi-element determination of dissolved metals at ultratrace level may be performed by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). U.S. EPA s Methods 200.8 and 1638 present a methodology for measuring trace elements in waters and wastes by the above technique. Sample is acid digested and the solution is introduced by pneumatic nebulization into a radio-frequency plasma. The elements in the compounds are atomized and ionized. The ions are extracted from the plasma through a differentially pumped vacuum interface and separated by a quadrupole mass spectrometer by their mass to charge ratios. The mass spectrometer must have a resolution capability of 1 amu peak width at 5% peak height. 

The nature of study objectives in environmental research is often multivariate. Several pollutant patterns from different, sometimes unknown, sources may occur. The state of pollution of a sampling point, line, or area in any environmental compartment, whether atmosphere, water, soil, or biota, depends mostly on the nature of the different sources of pollution. Stack emissions are characterized by a multi-element pattern. Waste water effluents contain different contaminants, ranging from heavy metals to cocktails of organic compounds. 

Analysis the process of investigation of a sample of the physical world to learn about its chemical components, composition, structure, or other physical or chemical characteristics. Generally only samples are analyzed and individual elements, compounds, and ions are separated from one another, identified, measured, or determined. A pure compound or multi-element ion is analyzed only when it is investigated to determine its components, composition, structure, or other physical or chemical characteristics. 

Isomers two or more compounds or multi-element ions that have the same elemental composition but different structures. 

Four techniques based on mass spectrometry are widely used for multi-elemental trace analysis of inorganic compounds in a wide range of sample types. These techniques are thermal ionization (TI), spark source (SS), glow discharge (GD) and inductively coupled plasma (ICP) mass spectrometry. In these techniques, atomization and ionization of the analysed sample are accomplished by volatilization from a heated surface, attack by electrical discharge, rare-gas ion sputtering and vaporization in a hot flame produced by inductive coupling. 

The association of a spectrometer with a liquid chromatograph is usually to aid in structure elucidation or the confirmation of substance identity. The association of an atomic absorption spectrometer with the liquid chromatograph, however, is usually to detect specific metal and semi-metallic compounds at high sensitivity. The AAS is highly element-specific, more so than the electrochemical detector however, a flame atomic absorption spectrometer is not as sensitive. If an atomic emission spectrometer or an atomic fluorescence spectrometer is employed, then multi-element detection is possible as already discussed. Such devices, used as a LC detector, are normally very expensive. It follows that most LC/AAS combinations involve the use of a flame atomic absorption spectrometer or an atomic spectrometer fitted with a graphite furnace. In addition in most applications, the spectrometer is set to monitor one element only, throughout the total chromatographic separation. 

Any emitting surface, cold-cathode, hotdevelop vapor pressures from the elements/compounds of their construction when heated. These vapors will also manifest themselves particularly during the initial start-up (breaking in) time of the lamp. Early atomic absorption, multi-element lamps were shown to have this problem. Some of these additives specifically react with residual gases and elements that might have a deleterious effect on lamp life. The electronics industry has used what are called "getter" substances in their tubes to remove some of these substances and improve emission. 

At irradiation with thermal neutrons, stable isotopes of mercury and many other elements are converted into radioactive daughter isotopes, that can be identified and quantified by high resolution gamma spectrometry. The irradiation is usually carried out in a nuclear reactor with thermal neutron flux densities of lO -IO cm s NAA is well established as a multi-element technique, and has a reputation of good accuracy. Separation and specification of mercury compounds is, however, not possible, since organic mercury turns into inorganic at irradiation (Rottsohafer et al., 1971). 

The classical calibration of NAA methods involves comparison of sample activities with those of co-irradiated standards of the same element. Especially at multi-element analysis, the need for a large number of standards has limited the sample throughput capacity. To circumvent this, alternative calibration techniques have been elaborated. The single comparator method makes multi-element determinations possible, by use of a single element standard (neutron flux monitor). The mass of the analyte is calculated by use of an experimentally determined element-specific factor (k-value), valid for the analytical equipment in question (Girardi et al., 1965 Linekin, 1973 Simonits et al., 1975). Later, a more generalized standardization method, based on accurately determined constants for the active compound nuclei (ko-factors), and applicable to various analytical equipments, has been proposed (Moens et al., 1984 De Code et al., 1987). 

The thought of building several elements into one cathode occurred to workers in atomic absorption almost immediately after equipment became available. Initial eflForts were defeated mainly by the metallurgical naivete of the experiments. However, at the present time a considerable variety of multi-elements lamps are available, although they vary in usefulness. Depending on the metals involved, the cathodes are made from alloys, intermetallic compounds, or mixtures of powders sintered together. 

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