Analysis multi-element

It is frequently desirable to be able to determine the concentration of several elements simultaneously. Atomic absorption is then impractical, since different hollow-cathode lamps are required. Clearly, the atomic emission method is more suitable. However, a drawback with this technique is that thermal excitation in a flame is relatively poor, but alternative methods of excitation can be used. For a long time arcs or sparks have been used in metallurgical analysis. In this case the sample, which must be solid, forms one of the electrodes. 

In order to eliminate the drawback of being limited to solid samples a new type of excitation source, the Inductively Coupled Plasma (ICP) source, has been developed. The working principle for this source is illustrated in Fig.6.64. Three concentric quartz tubes carry flowing gases. An inductance coil, fed by an RF generator is placed around the upper end of. the outer 

The light emitted from the excitation source is dispersed and recorded by multiple photodetectors placed behind suitably located exit slits (Fig. 6.65). Fibre-optical techniques can also be used to collect light at a suitable location in the spectrometer focal plane for transmission to a battery of PMT.s. Calibration can be provided using standard solutions or standard electrodes. Using a computer-controlled data collection system the concentrations of the selected elements can be printed out shortly after the introduction of the sample. A complete system frequently incorporates means for automatic sample exchange. 

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Multielemental Analysis Atomic emission spectroscopy is ideally suited for multi-elemental analysis because all analytes in a sample are excited simultaneously. A scanning monochromator can be programmed to move rapidly to an analyte s desired wavelength, pausing to record its emission intensity before moving to the next analyte s wavelength. Proceeding in this fashion, it is possible to analyze three or four analytes per minute. 

The advantages of LA are now well-known - no sample preparation is needed, conducting and non-conducting samples of arbitrary structure can be analyzed directly, spatial resolution up to a few microns can be obtained, high vacuum conditions are not required, rapid simultaneous multi-element analysis is possible, and it is possible to obtain complete analytical information with a single laser pulse. A brief overview of the potential and limitations of LA will be given in this chapter. 

ICP-AES and ICP-MS analyses are hampered in almost all cases by the occurrence of sample matrix effects. The origins of these effects are manifold, and have been traced partly to physical and chemical aerosol modifications inside sample introduction components (nebulisation effects). Matrix effects in ICP-AES may also be attributed to effects in the plasma, resulting from easily ionised elements and spectral background interferences (most important source of systematic errors). Atomic lines are usually more sensitive to matrix effects than are ionic lines. There exist several options to overcome matrix interferences in multi-element analysis by means of ICP-AES/MS, namely ... 

Very efficient method for multi-element analysis of conducting solid samples... 

Applications ICP-MS has become the technique of choice for the determination of elements in a wide range of liquid samples at concentrations in the ng L 1 to [igL-1 range. Typical applications of ICP-MS are multi-element analysis of liquids (even with high solid contents) element speciation by hyphenation to chromatographic techniques continuous on-line gas analysis multi-element trace analysis of polymers and trace analysis in high-purity materials. ICP-MS is routinely used for quality control purposes. 

Entwistle, J. A. and P. W. Abrahams (1997), Multi-element analysis of soils and sediments from Scottish historical sites. The potential of inductively coupled plasma-mass spectrometry for rapid site investigation, /. Archaeol. Sci. 24, 407-416. 

The isotopic distribution of lead (IDMS) in shed teeth from children has been shown to be useful in studies of the history of exposure to lead, including the definition of the source of the exposure, e.g., mine dust vs. food (Gulson and Wilson 1994), so IDMS certainly has important applicability, if not for routine determinations. ICP/MS, however, is easier, more sensitive, allows for multi-element analysis, and provides isotopic data. 

Que Hee SS, Boyle JR. 1988. Simultaneous multi-elemental analysis of some environmental and biological samples by inductively coupled plasma atomic emission spectrometry. Anal Chem 60 1033-1042. 

Hollow-cathode lamps are currently available for over sixty elements. Several multi-element lamps have been constructed and are useful for routine determinations, but they have proved to be of doubtful performance up to now. More successful with regard to multi-element analysis have been computer controlled automated systems, which enable a programme of sequential measurements to be made with instrumental parameters being adjusted to the optimum for each element to be measured. 

The actual analysis of the samples started with a qualitative survey to identify the principal metals present. ICP-AES was selected as being most suitable for this because it provided a permanent record, a multi-element analysis, and good sensitivity. Solutions of the shellfish tissue were prepared for analysis by wet oxidation, and the sediments were digested with 40% v/v... 

COMPARATIVE MULTI-ELEMENTAL ANALYSIS OF MINERAL AND ECOLOGICAL COMPONENTS OF THE ECOSYSTEM "KARABASHTOWN" CO-EXISTING WITH A COPPER-SMELTING PLANT. PHYSICOCHEMICAL POINT OF VIEW 137 N.M. BARYSHEVA, N.V. GARMASHEVA, E. V. POLYAKOV, V.T. SURIKOV,V.N. UDACHIN... 

COMPARATIVE MULTI-ELEMENTAL ANALYSIS OF MINERAL AND ECOLOGICAL COMPONENTS OF THE ECOSYSTEM "KARABASHTOWN" CO-EXISTING WITH A COPPER-SMELTING PLANT. PHYSICOCHEMICAL POINT OF VIEW... 

COMP AM TIVE MULTI-ELEMENTAL ANALYSIS OF MINERAL 145... 

Durrant, S. F. (1992). Multi-element analysis of environmental matrices by laser ablation inductively coupled plasma mass spectrometry. Analyst 117 1585-1592. 

Entwhistle, J. A., Abrahams, P. W., and Dodgshon, R. A. (1998). Multi-element analysis of soils from Scottish historical sites. Interpreting land-use history through physical and geochemical analysis of soil. Journal of Archaeological Science 25 53-68. 

Graphite furnace Flame graphite furnace Varian Associates SpectrA A30 + 40 multi-element analysis Method storage SpectrA AI0 (low cost, single beam) SpectrA A20 (medium cost, double beam) SpectrA A300/400 multi-element analysis, centralized instrument control STA 95 and GTA 96 graphite tube atomizer units - compatible with ail SpectrA A instruments... 

Geological and geochemical applications of PXRF generally require multi-element analysis however, the more elements that are included within an analytical test, the greater the likelihood of problems such as peak overlaps or interferences, and manufacturers typically will provide machine calibrations for 20-30 elements in a particular analytical mode (see below). Our instruments have been calibrated for a range of elements for characterization of lithological units, different mineralization types and associated hydrothermal alteration, and other geochemical exploration vectors. 

This change reflects a growing awareness that chemical interactions between chemical species are important in complex chemical systems. Increased reliance on multi-elemental analysis reflects the ease with which such analyses can be performed. Recent advances in electronics, chemical instrumentation, and computerized data acquisition have quantitatively and qualitatively changed analytical chemistry. Chemists measure more variables and perform more experiments in less time than feasible just a few years ago. In spite of our recently acquired data affluence, many complex problems remain unsolved. The enhanced insight that additional dataware to provide has failed to materialize. In some cases, more data cloud the issue rather than clarify it. Acquiring massive quantities of data is ineffective until interpretations are made and incorporated into a mechanistic description of the system. 

All metals at trace concentration, or in trace quantities, can be analyzed by atomic absorption (AA) spectrophotometry in flame or graphite furnace (electrothermal reduction) mode. A rapid, multi-element analysis may use... 

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