Multielement simultaneous

This hyphenated technique has been successfully applied to the speciation of a number of metals, including lead, mercury, and tin. The advantages of determining multielements simultaneously and the wide dynamic liner range are obvious [13]. 

The common detector for AAS is the PMT. The construction and operation of a PMT has been described in Chapter 5. While PMTs are the most common detectors, solid-state single and multichannel detectors such as PDAs (discussed in Chapter 5) and CCDs (discussed in Chapter 7) are increasingly being used in AAS spectrometers. Many small systems, particularly those dedicated to one element such as a dedicated CVAAS mercury analyzer, use solid-state detectors instead of PMTs. Multielement simultaneous AAS systems also use multichannel solid-state detectors to measure more than one wavelength at a time. 

In Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), a gaseous, solid (as fine particles), or liquid (as an aerosol) sample is directed into the center of a gaseous plasma. The sample is vaporized, atomized, and partially ionized in the plasma. Atoms and ions are excited and emit light at characteristic wavelengths in the ultraviolet or visible region of the spectrum. The emission line intensities are proportional to the concentration of each element in the sample. A grating spectrometer is used for either simultaneous or sequential multielement analysis. The concentration of each element is determined from measured intensities via calibration with standards. 

ICP-OES is one of the most successful multielement analysis techniques for materials characterization. While precision and interference effects are generally best when solutions are analyzed, a number of techniques allow the direct analysis of solids. The strengths of ICP-OES include speed, relatively small interference effects, low detection limits, and applicability to a wide variety of materials. Improvements are expected in sample-introduction techniques, spectrometers that detect simultaneously the entire ultraviolet—visible spectrum with high resolution, and in the development of intelligent instruments to further improve analysis reliability. ICPMS vigorously competes with ICP-OES, particularly when low detection limits are required. 

G. M. Levy, A. Quaglia, R, E. Lazure, and S. W. McGeorge. Spect. Acta. 42B, 341, 1987. Describes the diode array-based spectrally segmented spectrometer for simultaneous multielement analysis. 

AED Simultaneous multielement Superior to FPD for quantitative analysis (S compounds) High sensitivity Versatile Expensive Requires skilled analysts [33]... 

The palladium and magnesium nitrates modifier has a substantial equalising effect on the atomisation temperature of the nine elements investigated. The optimum atomisation temperature for all but one element (thallium) is between 1900 and 2100 °C. This means that all elements can be determined at a compromise atomisation temperature of 2100 °C with a minimum sacrifice in sensitivity. Such uniform conditions for as many elements as possible are of vital importance if simultaneous multielement furnace techniques are envisaged. Moreover, in conventional graphite furnace AAS, uniform conditions for a number of elements can greatly facilitate and simplify daily routine analysis. 

Hiraide et al. [737] developed a multielement preconcentration technique for chromium (III), manganese (II), cobalt, nickel, copper (II), cadmium, and lead in artificial seawater using coprecipitation and flotation with indium hydroxide followed by ICP-AES. The metals are simultaneously coprecipitated with indium hydroxide adjusted to pH 9.5, with sodium hydroxide, ethano-lic solutions of sodium oleate and dodecyl sulfate added, and then floated to... 

Chong et al. [742] have described a multielement analysis of multicomponent metallic electrode deposits, based on scanning electron microscopy with energy dispersive X-ray fluorescence detection, followed by dissolution and ICP-MS detection. Application of the method is described for determination of trace elements in seawater, including the above elements. These elements are simultaneously electrodeposited onto a niobium-wire working electrode at -1.40 V relative to an Ag/AgCl reference electrode, and subjected to energy dispersive X-ray fluorescence spectroscopy analysis. Internal standardisation... 

This analytical method, based on TXRF, enables a large number of trace elements to be determined simultaneously. The range is suitable for different areas of the sea. The motivation to use TXRF resulted mainly from the characteristic features of the method its high detection power, its universal calibration curve, which eliminates the need for matrix-dependent standard samples or standard-addition procedures, the simple preparation of the sample films, and of course the possibility of multielement determination. 

N. Jakubowski, D. Stuewer and W. Vieth, Performance of a glow discharge mass spectrometer for simultaneous multielement analysis of steel, Anal. Chem., 59 (1987) 1825-1830. 

Unlike a flame, in which only a very limited number of metals emit light because of the low temperature, virtually all metals present in a sample emit their line spectrum from the ICP torch. Not only does this make for a very broad application for ICP, but it also means that a given sample may undergo very rapid and simultaneous multielement analysis. With this in mind, it is interesting to consider the options for the optical path for the ICP instrument. 

The advantage of ICP is that the emissions are of such intensity that it is usually more sensitive than flame AA (but less sensitive than graphite furnace AA). In addition, the concentration range over which the emission intensity is linear is broader. These two advantages, coupled with the possibility of simultaneous multielement analysis offered by the direct reader polychromator design, make ICP a very powerful technique. The only real disadvantage is that the instruments are more expensive. See Workplace Scene 9.3. 

A reliable authenticity assessment is concluded from the simultaneous consideration of multielement IRMS and enantioselective analysis. The differences of the stable isotope ratios of linalool and linalyl acetate are depicted as a three-dimensional plot of A values (d values of linalool minus d values of linalyl acetate for oxygen, hydrogen and carbon) (Fig. 17.15). This plot shows that the commercial samples S1-S5 are different from all the other samples investigated. Linalool and linalyl acetate of S1-S5 definitely are not genuine lavender oil compounds. 

L. Ebdon, M. Foulkes and K. O Hanlon, Optimised simultaneous multielement analysis of environmental slurry samples by inductively coupled plasma atomic emission spectrometry using a segmented array charge-coupled device detector. Anal. Chim. Acta, 311, 1995, 123-134. 

K. S. Farah and J. Sneddon, Optimisation of a simultaneous multielement atomic absorption spectrometer, Talanta, 40(6), 1993, 879-882. 

The inductively coupled plasma13 shown at the beginning of the chapter is twice as hot as a combustion flame (Figure 21-11). The high temperature, stability, and relatively inert Ar environment in the plasma eliminate much of the interference encountered with flames. Simultaneous multielement analysis, described in Section 21 1. is routine for inductively coupled plasma atomic emission spectroscopy, which has replaced flame atomic absorption. The plasma instrument costs more to purchase and operate than a flame instrument. 

An inductively coupled plasma emission spectrometer does not require any lamps and can measure as many as —70 elements simultaneously. Color Plates 23 and 24 illustrate two designs for multielement analysis. In Plate 23, atomic emission enters the polychromator and... 

Depth profile of elements in seawater near hydrothermal vents. [From T. Akagi and H. Haraguchi, Simultaneous Multielement Determination of Trace Metals Using W mL of Seawater by Inductively Coupled Plasma Atomic Emission Spectrometry with Gallium Coprecipitation and Microsampling Technique Anal. Chem. 1990, 62.81.]... 

Metals can be conveniently determined by emission spectroscopy using inductively coupled plasma (ICP). A great advantage of ICP emission spectroscopy as applied to environmental analysis is that several metals can be determined simultaneously by this method. Thus, multielement analysis of unknown samples can be performed rapidly by this technique. Another advantage is that, unlike atomic absorption spectroscopy, the chemical interference in this method is very low. Chemical interferences are generally attributed to the formation of molecular compounds (from the atoms) as well as to ionization and thermochemical effects. The principle of the ICP method is described below. 

Multielement determination (sequential or simultaneous) faster analysis time minimal chemical interaction detection limits and sensitivity fall in between that of flame and graphite furnace measurements. 

Comparison with the highest possible values of a multivariate random correlation (see also Section 6.6.3) shows a correlation period of approximately two weeks and two days. This means that sampling of suspended dust at intervals of two weeks is sufficient for the characterization of the average impact of multielement emissions (for all investigated elements simultaneously) at that particular sampling point. 

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