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Element-specific atomic emission chromatographic detection for food and environmental analysis
Abstract
Speciation has become an important area of research in the fields of food and environmental analysis because the nutritional value and toxicity of an element depend largely on its chemical form. Elemental speciation requires an efficient separation procedure followed by elementally selective detection. Atomic plasma spectral emission spectroscopy provides powerful element-specific detection for gas chromatography (GC-AED), and today it is utilized in the only commercial available instrument which can be used for both metal and nonmetal speciation. GC-AED has the important advantage of high sensitivity, high elemental selectivity and the possibility of simultaneous multi-element analysis. The atomic emission detection response can flag compounds in the GC effluent which contain specific elements even though these compounds may be present in very small amounts or may co-elute with other components. This dissertation research has been focused on the application of different sample pre-treatment methods coupled with GC-AED for the speciation of organo-selenium in garlic, onion and broccoli. Interest in selenium has heightened in recent years concomitant with the recognition of the element's essential nutritional role, and upon reports of selenium toxicity in humans. Chemical and biochemical pathways in the natural selenium cycle are still not clear because it is very difficult to identify the form of organoselenium compounds at naturally occurring levels. Speciation of organo-selenium compounds at natural levels requires very sensitive and selective detection following an efficient separation and isolation process. Allium species, in particular garlic, have been investigated for a long time. The beneficial properties of garlic feature in the folklore of many cultures around the world. Recently, health benefits of garlic and other related plants, such as onion and broccoli, have been thought to derive from various sulfur- and perhaps selenium-containing compounds in these plants. Identification of the selenium-containing compounds has remained elusive because nature plants contain selenium at levels of less than one ppm, which are orders of magnitude lower than the levels of sulfur present. A large number of papers have been published regarding sulfur chemistry of Allium, but very little information is available on their selenium chemistry. GC-AED was used to achieve the first successful identification and determination of organoselenium compounds at natural levels in plants, these including garlic, onion, broccoli, Chinese chive and radish. Headspace-GC-AED was used to determine trace levels of volatile organoselenium compounds. This has given information on the likely enzymatic degradation of selenium compounds in natural plants. Tenax trap/cryogenic-GC-AED has been used to measure organoselenium compounds in human breath after ingestion of garlic. This has helped the understanding of selenium degradation pass ways in human beings. Another investigation has focussed upon the primarily chemical format of selenium in natural plants; derivatization-GC-AED was used for the determination of free seleno-amino acids. This dissertation also discussed the application of headspace-GC-AED for the determination of 'organo-mercury' in water. Sub-parts per trillion of alkylmercury compounds have been detected in environmental water samples. GC-AED and a membrane introduction mass spectrometer (MIMS) have been used for the study of mechanisms of enzymatic degradation in garlic, major sulfur volatiles released from garlic having been monitored. HPLC-ICP-MS has been investigated for the determination of non-volatile organo-selenium compounds. Investigation on improving the performance of GC-AED were also a part of this research.
Subject Area
Analytical chemistry|Food science|Nutrition
Recommended Citation
Cai, Xiaojia, "Element-specific atomic emission chromatographic detection for food and environmental analysis" (1996). Doctoral Dissertations Available from Proquest. AAI9638938.
https://scholarworks.umass.edu/dissertations/AAI9638938