Fluorescence spectrometry, atomic

A simplified model for the fluorescence process can be drawn up for two levels [662]. When a two-level system is considered (Fig. 125) and excitation is expected to occur only as a result of absorption of radiation with radiant density without any contributions from collision processes to the excitation, the population of the excited level (112) can be given by  

In the case of primary sources with low intensity and atom reservoirs at low pressure, e.g. glow discharges in which quenching is low  

When the primary source is of a low intensity and quenching occurs in the atom reservoir, as is the case in an atmospheric pressure furnace, flame or plasma  

When the absorption of radiation increases up to a certain value A21 and k2i become negligible. Then U2 = nx/2 and becomes independent of the radiant density of the exciting radiation and a state of saturation is reached. This situation can be realized when lasers are used as primary sources. 

The radiaton density required to obtain saturation can be calculated as  

Atomic fluorescence spectrometry (AFS) is based on the excitation of gaseous atoms by optical radiation of suitable wavelength (frequency) and the measurement of the resultant fluorescence radiation. Atomic fluorescence is, thus, in principle the opposite process to atomic absorption. Each atom has a characteristic fluorescence spectrum. The wavelength of the fluorescence line may be the same, greater, or smaller than the wavelength of the excitation line. 

The resonance fluorescence is the most common form, and in this case the excitation and fluorescence lines have the same wavelength. The resonance fluorescence lines may originate from the ground state or from an excited state. 

If the wavelength of the fluorescence line is greater than that of the excitation line, the effect is called Stokes direct line fluorescence. In the 

In the case of the stepwise line fluorescence, the effect is divided into Stokes and anti-Stokes stepwise fluorescence depending on the wavelength (energy) relationships. A thermally assisted process may take place, if after radiation excitation, further collisional excitation occurs. 

The intensity of atomic fluorescence depends on the intensity of the incident radiation source, concentration of the analyte atoms in the ground state, absorption efficiency of the incident radiation, and degree of selfabsorption in the atomization cell. 

Principles and Characteristics Atomic fluorescence spectrometry (AFS) is based on excitation of atoms by radiation of a suitable wavelength (absorption), and detection and measurement of the resultant de-excitation (fluorescence). The only process of analytical importance is resonance fluorescence, in which the excitation and fluorescence lines have the same wavelength. Nonresonance transitions are not particularly analytically useful, and involve absorption and fluorescence photons of different energies (wavelength). 

In AFS, the analyte is introduced into an atomiser (flame, plasma, glow discharge, furnace) and excited by monochromatic radiation emitted by a primary source. The latter can be a continuous source (xenon lamp) or a line source (HCL, EDL, or tuned laser). Subsequently, the fluorescence radiation is measured. In the past, AFS has been used for elemental analysis. It has better sensitivity than many atomic absorption techniques, and offers a substantially longer linear range. However, despite these advantages, it has not gained the widespread usage of atomic absorption or emission techniques. The problem in AFS has been to obtain a 

AFS instruments are mainly used to detect the vapour-forming elements, such as those that form hydrides (As, Bi, Ge, Pb, Se, Sb, Sn and Te). AFS is less prone to spectral interferences than either AES or A AS. Detection limits in AFS are low, especially for elements with high excitation energies, such as Cd, Zn, As, Pb, Se and Tl. In recent years, the use of AFS has been boosted by the production of specialist equipment that is capable of determining individual analytes at very low concentrations (at the ng L-1 level). The analytes have tended to be introduced in a gaseous form. AFS methods and instrumentation have been reviewed [214-216], see also ref. [17]. 

Applications No reference to polymer/additive problem solving by AFS has been recorded. 

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The very low Hg concentration levels in ice core of remote glaciers require an ultra-sensitive analytical technique as well as a contamination-free sample preparation methodology. The potential of two analytical techniques for Hg determination - cold vapour inductively coupled plasma mass spectrometry (CV ICP-SFMS) and atomic fluorescence spectrometry (AFS) with gold amalgamation was studied. 

DETERMINATION OF ARSENIC (As) IN NATURAL AND WASTE WATER USING HIDRIDE GENERATION ATOMIC FLUORESCENCE SPECTROMETRY... 

Arsenic is both toxic and cai cinogenic element. It is necessary to have a fast, reliable and accurate method for determination of ai senic in water. The hydride-generation atomic fluorescence spectrometry (HG AFS) is one of the simple and sensitive techniques for the determination of this element in various types of waters. 

In this work, atomic fluorescence spectrometry (AFS) with vapor generation is used for Hg determination in different types of waters (drinking, surface, underground, industrial waste). 

Montaser, A., Goode, S. R., and Crouch, S. R. "Graphite Braid Atomizer for Atomic Absorption and Atomic Fluorescence Spectrometry . Anal. Chem. (1974), 46, 599-601. 

For PHg, a variety of different filter methods have been applied, such as Teflon or quartz fiber filters. Before analysis, these filters undergo a wet chemical digestion usually followed by reduction-volatilization of the Hg to Hg(0) and analysis using cold vapor atomic absorbance spectrometry (CVAAS) or cold vapor atomic fluorescence spectrometry (CVAFS). Recently, a collection device based on small qrrartz... 

Both emission and absorption spectra are affected in a complex way by variations in atomisation temperature. The means of excitation contributes to the complexity of the spectra. Thermal excitation by flames (1500-3000 K) only results in a limited number of lines and simple spectra. Higher temperatures increase the total atom population of the flame, and thus the sensitivity. With certain elements, however, the increase in atom population is more than offset by the loss of atoms as a result of ionisation. Temperature also determines the relative number of excited and unexcited atoms in a source. The number of unexcited atoms in a typical flame exceeds the number of excited ones by a factor of 103 to 1010 or more. At higher temperatures (up to 10 000 K), in plasmas and electrical discharges, more complex spectra result, owing to the excitation to more and higher levels, and contributions of ionised species. On the other hand, atomic absorption and atomic fluorescence spectrometry, which require excitation by absorption of UV/VIS radiation, mainly involve resonance transitions, and result in very simple spectra. 

Auger electron spectroscopy Phosphorous/nitrogen-selective alkali/flame ionisation detector Atomic force microscopy Atomic fluorescence spectrometry All-glass heated inlet system... 

Yuzefovsky et al. [241] used Cis resin to preconcentrate cobalt from seawater prior to determination at the ppt level by laser-excited atomic fluorescence spectrometry with graphite electrothermal atomiser. 

Laser-excited atomic fluorescence spectrometry has been used to determine down to 1 ng/1 of lead in seawater [359]. 

Cobalt Co(III) adsorbed on C18 bonded silica Laser excited atomic fluorescence spectrometry - [241]... 

It has been reported that the differential determination of arsenic [36-41] and also antimony [42,43] is possible by hydride generation-atomic absorption spectrophotometry. The HGA-AS is a simple and sensitive method for the determination of elements which form gaseous hydrides [35,44-47] and mg/1 levels of these elements can be determined with high precision by this method. This technique has also been applied to analyses of various samples, utilising automated methods [48-50] and combining various kinds of detection methods, such as gas chromatography [51], atomic fluorescence spectrometry [52,53], and inductively coupled plasma emission spectrometry [47]. 

Techniques for analysis of different mercury species in biological samples and abiotic materials include atomic absorption, cold vapor atomic fluorescence spectrometry, gas-liquid chromatography with electron capture detection, and inductively coupled plasma mass spectrometry (Lansens etal. 1991 Schintu etal. 1992 Porcella etal. 1995). Methylmercury concentrations in marine biological tissues are detected at concentrations as low as 10 pg Hg/kg tissue using graphite furnace sample preparation techniques and atomic absorption spectrometry (Schintu et al. 1992). 

Atomic fluorescence spectrometry has a number of potential advantages when compared to atomic absorption. The most important is the relative case with which several elements can be determined simultaneously. This arises from the non-directional nature of fluorescence emission, which enables separate hollow-cathode lamps or a continuum source providing suitable primary radiation to be grouped around a circular burner with one or more detectors. 

Total dissolved Fe and Mn were analyzed directly by flame atomic absorption spectrometry (AAS). As was measured by AAS with hydride generation (HG-FIAS). Total dissolved Se concentrations were determined by hydride-generation atomic fluorescence spectrometry (Chen etal., 2005). 

Analytical Techniques Atomic absorption spectrometry, 158, 117 multielement atomic absorption methods of analysis, 158, 145 ion microscopy in biology and medicine, 158, 157 flame atomic emission spectrometry, 158, 180 inductively coupled plasma-emission spectrometry, 158, 190 inductively coupled plasma-mass spectrometry, 158, 205 atomic fluorescence spectrometry, 158, 222 electrochemical methods of analysis, 158, 243 neutron activation analysis, 158, 267. 

Graphite furnace used for atomic fluorescence spectrometry. 

Atomic fluorescence spectrometry is based on the absorption of optical radiation of suitable frequency (wavelength) by gaseous atoms and the resultant deactivation of the excited atoms with the release of radiation. The frequencies (wavelengths) emitted are characteristic of the atomic species. 

Table B.2 Instrumental conditions for hydride generation atomic fluorescence spectrometry.

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