Analyte emission

Nygaard [752] has evaluated the application of the Spectraspan DC plasma emission spectrometer as an analysis tool for the determination of trace heavy metals in seawater. Sodium, calcium, and magnesium in seawater are shown to increase both the background and elemental line emission intensities. Optimum analytical emission lines and detection limits for seven elements are reported in Table 5.8. 

Scattering of excitation light in the direction of the detector and of the emitted light can influence the precision of the measurement. At very high concentration of analyte, emission may not be seen because most of the exciting light is absorbed near the wall of the sample cell. The fact is that most molecules do not fluoresce and cannot be... 

It is also possible to use an internal standard to correct for sample transport effects, instrumental drift and short-term noise, if a simultaneous multi-element detector is used. Simultaneous detection is necessary because the analyte and internal standard signals must be in-phase for effective correction. If a sequential instrument is used there will be a time lag between acquisition of the analyte signal and the internal standard signal, during which time short-term fluctuations in the signals will render the correction inaccurate, and could even lead to a degradation in precision. The element used as the internal standard should have similar chemical behaviour as the analyte of interest and the emission line should have similar excitation energy and should be the same species, i.e. ion or atom line, as the analyte emission line. 

Based on the configurations in Figure 1.5, many analytical techniques have been developed employing different atomisation/excitation sources. For example, two powerful AAS techniques are widespread one uses the flame as atomiser (FAAS) whereas the other is based on electrothermal atomisation (ETAAS) in a graphite furnace. Although the flame has limited application in OES, many other analytical emission techniques have evolved in recent decades based on dilTerent atomisation/excitation plasma sources. 

During the 20-plus years that mass spectrometrists lost interest in glow discharges, optical spectroscopists were pursuing these devices both as line sources for atomic absorption spectroscopy and as direct analytical emission sources [6-10]. Traditionally, inorganic elemental analysis has been dominated by atomic spectroscopy. Since an optical spectrum is composed of lines corre-... 

The direct determination of some major elements (Ca, K, Mg, Na, and P) and Zn by ICP-AES was performed in powdered milk [14]. Samples were diluted with a 5 or 10 percent (v/v) water-soluble, mixed tertiary amine reagent at pH 8. This reagent mixture dissociated casein micelles and stabilized liquid phase cations. No decrease in analyte emission intensities was observed. Reference solutions were prepared in 10 percent (v/v) mixed amine solution, and no internal reference element was needed for ICP-AES. The direct technique is as fast as slurry approaches, without particle size effects or sensitivity losses. 

Barnett, Fassel, V.A. and Knisely, R.N. (1968) Theoretical principles of internal standardisation in analytical emission, Spectrochimica Acta, 23A, p643. 

Modulation is defined as the changing of some property of a carrier wave by the desired signal in such a way that the carrier wave can be used to convey information about the signal. Properties that are typically altered are frequency, amplitude, and wavelength. In AAS. the source radiation is amplitude modulated, but the background and analyte emission are not and are observed as dc signals. 

The excitation temperature describes the population of the excited levels of atoms and ions. Therefore it is important in studies on the dependence of analyte line intensities on various plasma conditions in analytical emission spectrometry. 

Advantages of AES, relative to flame-AAS, include the lack of a requirement for a radiation source. Collisions within the plasma serve to promote analyte atoms to excited state levels. Additionally, this technique is characterised by linearities of response which span three to four orders of magnitude. Limits of detection for ICP-AES are similar to those obtained with flame-AAS (typically within a factor of 3 to 5 - some elements are shghtly less responsive in flame-AAS others slightly more responsive). ICP-AES does require a fairly high resolution monochromator/detection system to scan carefully across analyte emission lines and to be able to resolve them from the other emissions and from the high luminosity of the torch. There are many spectral... 

ScHRENK WG (1988) Historical development of high-energy excitation sources for analytical emission spectroscopy. Appl Spectrosc 42 4-11. 

In the B panel the matrix overlaps the analyte emission line with no magnetic field. When the magnetic field is applied, this overlap is reduced and the matrix will have been undercorrected by the Zeeman system. In this case the matrix will cause a signal even when no analyte is present. 

Barnes, R. M. Emission Spectroscopy, Grove, E. L., ed. Analytical Emission Spectros-Anal. Chem., 44, 122R (1972) 46, 150R copy, vol. 1, parts I and II. New York ... 

Mika, J., and Torok, T. Analytical Emission Spectroscopy, New York Crane, Russak, Co., 1974. 

In the period 1860-1900 a number of practical advances in analytical emission spectroscopy occurred. In 1874, Lockyer stated that the length, brightness, thickness, and number of spectral lines were related to the quantity of the element present in the sample. Hartley s studied the spectra of metals at varying concentrations and proposed a method of analysis based on the last line principle. The most persistent lines were those visible at the lowest concentrations of the element and thus served to measure the lowest concentration of the element that produced spectral lines under controlled excitation conditions. 

The early use of a flame as an excitation source for analytical emission spectroscopy dates back to HerscheF and Talbot, who identified alkali metals by flame excitation. The work of Kirchhoff and Bunsen also was basic to the establishment of this technique of atomic excitation. One of the earliest uses of flame excitation was for the determination of sodium in plant ash (1873) by Champion, Pellet, and Grenier.Thus use of the flame paralleled that of arc and spark excitation in the 1800 s. 

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