Atomic Emission Techniques

FIGURE 18.8 Graphite furnace for atomic absorption analysis, and typical output signal. 

FIGURE 18.9 Schematic diagram showing inductively coupled plasma used for optical emission 

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Various forms of off- and on-line AES/AAS can achieve element specific detection in IC. The majority of atomic emission techniques for detection in IC are based on ICP. In the field of speciation analysis both IC-ICP-AES and IC-ICP-MS play an important role. Besides the availability of the ICP ion source for elemental MS analysis, structural information can be provided by interfaces and ion sources like particle beam or electrospray. 

Spectral line sources are used as light sources in atomic absorption instruments rather than the continuum sources used for UV-VIS molecular absorption instruments, and several atomic emission techniques require no light source at all apart from the thermal energy source. 

Name two techniques that are atomic absorption techniques and two that are atomic emission techniques. 

Most common atomic absorption techniques flame atomic absorption and graphite furnace atomic absorption. Most common atomic emission techniques ICP and flame emission. 

Although AFS combines, for some elements, the advantages of the large linear dynamic range typical of atomic emission techniques and the high selectivity of atomic absorption, the method has so far not found widespread use. 

Miyahara M, Suzuki T, Saito Y. 1992. Multiresidue method for some pesticides in lanolin by capillary gas chromatography with detection by electron capture, flame photometric, mass spectrometric, and atomic emission techniques. J Agric Fd Chem 40 64-69. 

A comprehensive review of directly coupled gas chromatography-atomic spectroscopy applications has been published [128]. This review list over 100 references classified according to the detection technique and is highly recommended. Another excellent review outlines the advances in interfacing and plasma detection [130]. A review of the gas chromatographic detection of selected trace elements (mercury, lead, tin, selenium, and arsenic) has been published. This article reviews the many different detection methods available including atomic emission techniques [131]. 

Glow-discharge-atomic emission techniques (GD-AE) for solid analysis are instru-mentally simpler and more inexpensive than GD-MS [200], Major trade-offs, however, include poorer limits of detection and reduced elemental coverage. Although compact commercial GD-AE instruments were popular in Europe during the 1980s, their use in the USA remained modest until the 1990s. 

Spectroscopic detection (using ultraviolet/visible (UV/vis) absorbance, refractive index, fluorescence, atomic absorption or atomic emission). Techniques based on postcolumn reactions. 

In this chapter, we first present a theoretical discussion of the sources and properties of optical atomic spectra. We then list methods used for producing atoms from samples for elemental analysis. Finally, we describe in some detail the various techniques used for introducing samples into the devices that arc used for optical absorjHion, emis-, sion, and fluorescence spectrometry as well as atomic mass spectrometry. Chapter 9 is devoted to atormc.absorption methods, the most widely used of all the. atomic spectrometric techniques. Chapter 10 deals with several types of atomic emission techniques. Brief chapters on atomic mass spectrometry and atomic X-ray methods follow this discussion. 

Rotrode Filter Spectroscopy (RFS) is a recently improved technique that has been shown in actual freld applications to provide important additional information about large wear particles, information that may be missed with conventional techniques. It is applied with existing instruments to provide two analyses on the same used oil sample. The first, using the standard RDE atomic emission technique, detects and quantifies dissolved and small wear metals and contaminants. The second analysis, by RFS, qualifies and serai-quantifies larger particles. This paper has shown how the early version of the RFS system has been improved and updated to provide better sensitivity, repeatability, faster sample throughput, and improved particle capture capability. 

Lukas, M. and Giering, L. P., The Effects of Metal Particle Size in the Analysis for Wear Metals Using the Rotating Disc Atomic Emission Technique, International Symposium on Oil Analysis, Erding, Germany, July 1978. 

AES would be expected to suffer from chemical interferences and spectral interferences, as do the other atomic emission techniques we have discussed. The focus will be on the commercial instmments available and on the graphite furnace-laser system. 

The quantification of electrolytes, notably through flame photometric (atomic emission) techniques, may have some importance in forensic medicine. Indeed, different authors have reported the possibility of determining the time of death by the increase in concentration of some electrolytes and the decrease in certain others. 

The radiation source used in AAS is an HCL or an EDL, and a different lamp is needed for each element to be determined (except for the new continuum source system discussed earlier). Because it is essentially a single-element technique, AAS is not well suited for qualitative analysis of unknowns. To look for more than one element requires a significant amount of sample and is a time-consuming process. For a sample of unknown composition, multielement techniques such as XRF, ICP-mass spectrometry (ICP-MS), ICP-OES, and other atomic emission techniques are much more useful and efficient. 

Describe how LIBS works. What are the advantages of LIBS versus other atomic emission techniques ... 

In AFS, the excitation from the ground state to the upper state (Fig. 1C) is accomplished by absorption of a photon, and the measurement is made by detection of radiation emitted by the atom as it relaxes back from the excited state to the ground state. This re-emitted radiation is no different in character from the radiation emitted in the atomic emission technique. In AES, the atoms are excited only by the collisional energy inherent in the high temperature of the atom cell, while in AAS and AFS the atoms are excited primarily by radiation from an external light source. 

The use of plasma mass spectrometry for the detection of chromatographic eluates has been discussed. The combination of HPLC with ICP-MS detection provides an analjdical technique capable of providing species selectivity and sub-ng levels of detection. The superior detection levels, as compared to atomic emission techniques, should spur the development of both HPLC and GC procedures capable of speciating trace elements in environmental and clinical samples. Furthermore, the use of a helium microwave plasma source has been described. Preliminary studies have demonstrated the potential advantages of He MIP-MS for GC detection of halogenated compounds. 

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