Chromatographic detectors, atomic absorption fluorescence

Chlorophenols, determination of 102-104, 285, 350 Chlorophylls, determination of 104-106,203-205, 248-260 Chromatographic detectors, atomic absorption 32-33 fluorescence 29-31 infrared 31, 32 inductively coupled plasma atomic emission 33-35 Raman 31, 32 visible 29 Chromate, determination of 60-65 Chromium, determination of 166, 234, 235,477-481... 

Multielement analysis will become more important in industrial hygiene analysis as the number of elements per sample and the numbers of samples increases. Additional requirements that will push development of atomic absorption techniques and may encourage the use of new techniques are lower detction and sample speciation. Sample speciation will probably require the use of a chromatographic technique coupled to the spectroscopic instrumentation as an elemental detector. This type of instrumental marriage will not be seen in routine analysis. The use of Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) (17), Zeeman-effect atomic absorption spectroscopy (ZAA) (18), and X-ray fluorescence (XRF) (19) will increase in industrial hygiene laboratories because they each offer advantages or detection that AAS does not. 

The association of a spectrometer with a liquid chromatograph is usually to aid in structure elucidation or the confirmation of substance identity. The association of an atomic absorption spectrometer with the liquid chromatograph, however, is usually to detect specific metal and semi-metallic compounds at high sensitivity. The AAS is highly element-specific, more so than the electrochemical detector however, a flame atomic absorption spectrometer is not as sensitive. If an atomic emission spectrometer or an atomic fluorescence spectrometer is employed, then multi-element detection is possible as already discussed. Such devices, used as a LC detector, are normally very expensive. It follows that most LC/AAS combinations involve the use of a flame atomic absorption spectrometer or an atomic spectrometer fitted with a graphite furnace. In addition in most applications, the spectrometer is set to monitor one element only, throughout the total chromatographic separation. 

Besides the fractionation of metalloids through SEPs, a series of methods has been proposed for the determination of individual species in the various oxidation states (Gong et al., 2002 Kahakachchi et al., 2004). The most popular detectors for metalloid speciation are inductively coupled plasma-mass spectrometry (ICP-MS) and atomic fluorescence spectrometry (AES), especially after liquid chromatographic separation and hydride formation, which are increasingly replacing atomic absorption spectrometry (AAS). Speciation analysis of pollutants in terrestrial environments is, however, beyond our scope in this chapter. 

Currently, fewer ihan ten companies worldwide manufacture CH in.struments. Some two dozen companies offer supplies and accessories for CF. The initial cost of equipment and the expense of maintenance for CF are generally significantly lower than those for ion chromatographic and atomic spcctro.scopic instruments. I hus, commercial CF instruments with standard absorption or fluorescence detectors cost 10,(KK) to 65.(XK), Addition of mass spectromctric detection can raise the cost significantly. 

A range of chromatographic techniques coupled to element specific detectors has been used in speciation studies to separate individual organometallic species (e.g., butyltins, arsenic species) and to separate metals bovmd to various biomolecules. The combination of a chromatographic separation with varying instrumental detection systems are commonly called coupled, hybrid, or hyphenated techniques (e.g., liquid chromatography inductively coupled plasma-mass spectrometry (LC-ICP-MS), gas chromatography-atomic absorption spectroscopy (GC-AAS)). The detection systems used in coupled techniques include MS, ICP-MS, atomic fluorescence spectrometry (AFS), AAS, ICP-atomic emission spectrometry (ICP-AES), and atomic emission detection (AED). 

The utility of laser diodes for spectroscopic applications has been demonstrated in molecular absorption spectrometry, molecular fluorescence spectrometry, atomic absorption spectrometry, and as light sources for detectors in various chromatographic methods. Recent advances in laser diode technology fueled by consumer demand for high-speed, high-capacity DVD players have resulted in the availability of blue laser diodes with output powers up to 50 mW at 473 nm. These light sources are appearing routinely in commercial spectrometric systems. 

Radziuk, B., Thomassen, Y., Butler, L. R. P., Van Loon, J. C., Chau, Y. K., A Study of Atomic Absorption and Atomic Fluorescence Atomization Systems as Detectors in the Gas Chromatographic Determination of Lead, Anal. Chim. Acta 108 [1979] 31/8. 

Common gas chromatographic detectors that are not element- or metal-specific, atomic absorption and atomic emission detectors that are element-specific, and mass spectrometric detectors have all been used with the hydride systems. Flame atomic absorption and emission spectrometers do not have sufficiently low detection limits to be useful for trace element work. Atomic fluorescence [37] and molecular flame emission [38-40] were used by a few investigators only. The most frequently employed detectors are based on microwave-induced plasma emission, helium glow discharges, and quartz tube atomizers with atomic absorption spectrometers. A review of such systems as applied to the determination of arsenic, associated with an extensive bibliography, is available in the literature [36]. In addition, a continuous hydride generation system was coupled to a direct-current plasma emission spectrometer for the determination of arsenite, arsenate, and total arsenic in water and tuna fish samples [41]. 

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