Simultaneous atomic emission

Fig. 4.19. Simultaneous atomic emission detection using the CID array spectrometer of the complexes of Ca, Cu, and Mg following anion exchange chromatography.

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. 

Selectivity The selectivity of atomic emission is similar to that of atomic absorption. Atomic emission has the further advantage of rapid sequential or simultaneous analysis. 

Plasma sources were developed for emission spectrometric analysis in the late-1960s. Commercial inductively coupled and d.c. plasma spectrometers were introduced in the mid-1970s. By comparison with AAS, atomic plasma emission spectroscopy (APES) can achieve simultaneous multi-element measurement, while maintaining a wide dynamic measurement range and high sensitivities and selectivities over background elements. As a result of the wide variety of radiation sources, optical atomic emission spectrometry is very suitable for multi-element trace determinations. With several techniques, absolute detection limits are below the ng level. 

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. 

The emerging analytical technique of laser-induced breakdown spectroscopy (LIBS) is a simple atomic emission spectroscopy technique that has the potential for real-time man-portable chemical analysis in the field. Because LIBS is simultaneously sensitive to all elements, a single laser shot can be used to record the broadband emission spectra, which provides a chemical fingerprint of a material. 

All four dissolution procedures studied were found to be suitable for arsenic determinations in biological marine samples, but only one (potassium hydroxide fusion) yielded accurate results for antimony in marine sediments and only two (sodium hydroxide fusion or a nitricperchloric-hydrofluoric acid digestion in sealed Teflon vessels) were appropriate for determination of selenium in marine sediments. Thus, the development of a single procedure for the simultaneous determination of arsenic, antimony and selenium (and perhaps other hydride-forming elements) in marine materials by hydride generation inductively coupled plasma atomic emission spectrometry requires careful consideration not only of the oxidation-reduction chemistry of these elements and its influence on the hydride generation process but also of the chemistry of dissolution of these elements. 

The most convenient methods are those that permit simultaneous identification and quantitation of the test substance. Unfortunately these are relatively few in number but probably the best examples are in the area of atomic emission and absorption spectroscopy, where the wavelength of the radiation may be used to identify the element and the intensity of the radiation used for its quantitation. 

Chemically pure reagents were used. Cadmium was added as its sulfate salt in concentrations of about 50 ppm. Lanthanides were added as nitrates. For the experiments with other metal ions so-called "black acid from a Nissan-H process was used. In this acid a large number of metal ions were present. To achieve calcium sulfate precipitation two solutions, one consisting of calcium phosphate in phosphoric acid and the other of a phosphoric acid/sulfuric acid mixture, were fed simultaneously in the 1 liter MSMPR crystallizer. The power input by the turbine stirrer was 1 kW/m. The solid content was about 10%. Each experiment was conducted for at least 8 residence times to obtain a steady state. During the experiments lic iid and solid samples were taken for analysis by ICP (Inductively Coupled Plasma spectrometry, based on atomic emission) and/or INAA (Instrumental Neutron Activation Analysis). The solid samples were washed with saturated gypsum solution (3x) and with acetone (3x), and subsequently dried at 30 C. The details of the continuous crystallization experiments are given in ref. [5]. 

It is a remarkable fact that the contemporary history of absorption and emission spectroscopy began simultaneously, from the simultaneous discoveries that Bunsen and Kirchhoff made in the middle of the 19th century. They observed atomic emission and absorption lines whose wavelengths exactly coincided. Stokes and Kirchhoff applied this discovery to the explanation of the Fraunhofer spectra. Nearly at the same time approximately 150 years ago, Stokes explained the conversion of absorbed ultraviolet light into emitted blue light and introduced the term fluorescence. Apparently, the discovery of the Stokes shift marked the birth of luminescence as a science. 

Emission spectrum Radiation from an atom in an excited state, usually displayed as radiant power vs. wavelength. Each atom or molecule has a unique spectrum. The spectra can be observed as narrow line emission (atomic emission spectra) or as quasi-continuous emissions (molecular emission spectra). A mercury plasma emits both line spectra and continuous spectra simultaneously. 

A. M. Carro, I. Neira, R. Rodil and R. A. Lorenzo, Speciation of mercury compounds by gas chromatography with atomic emission detection. Simultaneous optimisation of a headspace solid-phase microextraction and derivatisation procedure by use of chemometric techniques, Chro-matographia, 56(11/12), 2002, 733-738. 

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. 

H. Karami, M. F. Mousavi, Y. Yamini and M. Shamsipur, On-line preconcentration and simultaneous determination of heavy metal ions by inductively coupled plasma-atomic emission spectrometry. Anal. Chim. Acta, 509(1), 2004, 89-94. 

Present atomic emission spectrophotometers allow multi-element analyses to be performed either simultaneously or sequentially. This ability is the result of progress made in optics, excitation sources, detectors and microcomputers. Atomic emission, which was initially used in the metallurgical industry, has now expanded into many areas and competes with atomic absorption. 

Figure 15.8—Coupling of a gas chromatograph with an atomic emission spectrophotometer. Effluents from the capillary column are injected into the plasma and decomposed into their elements. Each chromatogram corresponds to the compound containing the element of interest. For a given retention time, indication as to the elements included in a compound can be obtained. The plasma in this example is generated by heating the carrier gas (He) with a microwave generator confined in a cavity at the exit of the column. A diode array detector system can be used for simultaneous detection of many elements (chromatograms courtesy of a Hewlett Packard document).

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.]... 

Color Plate 23 Polychromator for Inductively Coupled Plasma Atomic Emission Spectrometer with One Detector for Each Element (Section 21-4) Light emitted by a sample in the plasma enters the polychromator at the right and is dispersed into its component wavelengths by grating at the bottom of the diagram. Each different emission wavelength (shown schematically by colored lines) is diffracted at a different angle and directed to a different photomultiplier detector on the focal curve. Each detector sees only one preselected element, and all elements are measured simultaneously. [Courtesy TJA Solutions, Franklin, MA.J... 

Thus, the conductivity of any aqueous sample may be precisely calculated, as we see in the above two examples, if we know the concentrations of the metal ions and the anions in the sample. The presence of such metal ions and the anions and their concentrations may be simultaneously measured by ICP atomic emission spectrophotometer and ion chromatograph, respectively. 

Perez-Sirvent, C. and M.-J. Martlnez-Sanchez. 2007. Comparison of two derivatizing agents for the simultaneous determination of selenite and organoselenium species by gas chromatography and atomic emission detection after preconcentration using solid-phase microextraction. J. Chromatogr. A 1165 191-199. 

Figure 7 illustrates the usefulness of this optical arrangement. Radiation from a multielement hollow cathode lamp containing Mn and Cr was allowed to fall on one fiber-optic strand. Radiation from a second hollow cathode lamp containing Li was incident on a second fiber optic strand. Individual and composite spectra are shown in the figure. With this optical system, lithium can be determined simultaneously with Cr and Mn by atomic emission, or lithium could be used as an internal standard for the analysis. To do this with a conventional one-dimensional dispersive system would require a wavelength window from 403 nm to 671 nm, resulting in poor resolution. 

Simultaneous Multielement Determinations by Atomic Absorption and Atomic Emission with a Computerized Echelle Spectrometer/Imaging Detector System... 

Judging from the degree of apparent interest and the number of papers published in the field of elemental TOF-MS over the last 3-4 years, it appears that this marriage is one full of promise for the future of elemental analysis. Perhaps the primary reason for such a trend is the need for a truly simultaneous mass spectrometer capable of extending capabilities beyond current instrumentation. The fields of ICP and GD atomic emission spectroscopy have been revolutionized by the incorporation of simultaneous array detectors. This revolution is just now beginning in the mass spectrometry field. 

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