Plasma emission spectroscopy chemical speciation

Plasma emission spectroscopy is an elemental analysis technique that is, it provides no information on the chemical form or oxidation state of the element being determined. The identification of the chemical state of an element in a sample is called speciation. For example, in environmental samples, mercury may exist in a variety of species mercuric ion, mercurous ion, methymercury compounds, and the extremely toxic compound dimethyhnercury. Determination of mercury by ICP-OES results in total mercury concentration chemical speciation would teU us how much mercury is present in each of the different forms. Arsenic is another element of environmental and health interest because of its toxicity. Arsenic, like mercury, exists in multiple organoarsenic compounds and multiple oxidation states as inorganic arsenic ions. Why is speciation... 

A number of very useful and practical element selective detectors are covered, as these have already been interfaced with both HPLC and/or FIA for trace metal analysis and spe-ciation. Some approaches to metal speciation discussed here include HPLC-inductively coupled plasma emission, HPLC-direct current plasma emission, and HPLC-microwave induced plasma emission spectroscopy. Most of the remaining detection devices and approaches covered utilize light as part of the overall detection process. Usually, a distinct derivative of the starting analyte is generated, and that new derivative is then detected in a variety of ways. These include HPLC-photoionization detection, HPLC-photoelectro-chemical detection, HPLC-photoconductivity detection, and HPLC-photolysis-electrochemical detection. Mechanisms, instrumentation, details of interfacing with HPLC, detector operations, as well as specific applications for each HPLC-detector case are presented and discussed. Finally, some suggestions are provided for possible future developments and advances in detection methods and instrumentation for both HPLC and FIA. 

Several methods are available for the determination of total aluminum in biological and other materials. Chemical and physicochemical methods are in most practical situations insensitive and inaccurate X-ray fluorescence is specific but lacks sensitivity neutron activation analysis is complex and subject to interferences, although it is a very sensitive technique. Nuclear magnetic resonance spectroscopy is not very sensitive but useful to get information on speciation [33]. Graphite furnace atomic absorption spectrometry (GFAAS) is the most widely used technique and can produce reliable results, provided that the matrix effects are recognized and corrected. Savory and Wills [19] reviewed chemical and physicochemical methods for the determination of aluminum in biological materials, e.g. X-ray fluorescence, neutron activation analysis, atomic emission spectrometry, flame emission, inductively coupled plasma emission spectroscopy, and AAS. 

Instrumental Quantitative Analysis. Methods such as x-ray spectroscopy, oaes, and naa do not necessarily require pretreatment of samples to soluble forms. Only reUable and verified standards are needed. Other instmmental methods that can be used to determine a wide range of chromium concentrations are atomic absorption spectroscopy (aas), flame photometry, icap-aes, and direct current plasma—atomic emission spectroscopy (dcp-aes). These methods caimot distinguish the oxidation states of chromium, and speciation at trace levels usually requires a previous wet-chemical separation. However, the instmmental methods are preferred over (3)-diphenylcarbazide for trace chromium concentrations, because of the difficulty of oxidizing very small quantities of Cr(III). 

Childress, W.L., Erickson, D. and Krull, I.S. (1992) Trace selenium speciation via high-performance liquid chromatography with ultraviolet and direct-current plasma emission detection. In Element-specific Chromatographic Detection by Atomic Emission Spectroscopy (ed. Uden, PC.). American Chemical Society, Washington, DC, pp. 257-273. 

All major modern atomic absorption and emission techniques and instrumentation are covered. Appendices with FAAS and GFAAS conditions have been added, and a new appendix with up-to-date hmits of detection for all the atomic spectroscopic techniques is included. Chemical speciation using hyphenated chromatographic-atomic emission spectroscopy is described as is a novel microwave induced plasma emission instrument for particle characterization. 

WL. Childress, D. Erickson, and I.S. Krull. Selenium speciation in dietary mineral supplements and foods by gas/liquid chromatography interfaced with direct current plasma emission spectroscopic detection (GC/HPLC-DCP). Element Spedfic Chromatographic Detection by Atomic Emission Spectroscopy, ACS Symposium Series, Ed. by PC. Uden, American Chemical Society, Washington, DC, 1991, submitted for publication. 

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