Extraction chemical fractionation techniques

According to International Union of Pure and Applied Chemistry (IUPAC), the terms speciation and chemical species should be reserved for the forms of an element defined as to isotopic composition, electronic or oxidation state and/or complex or molecular structure (Templeton el al, 2000). This classical definition, appropriate to speciation in solution samples, would exclude most speciation studies on solid materials, such as soils and sediments, more properly defined as fractionation studies. The terminology used in this chapter is based on the broader definition of speciation given by Ure and Davidson (2002), which encompass the IUPAC s narrow definition and includes the selective extraction and fractionation techniques of solid samples. 

Sequential extraction or chemical fractionation techniques have been widely used in the characterization of various phosphorus fractions in soils and sediments, with an emphasis on the more bioavailable or plant-available inorganic forms (Condron et al., 2005). Early extraction procedures (Chang and Jackson, 1957 Williams et al., 1976b) focused on inorganic phosphorus associated with iron, aluminium and calcium, using various acid, base or salt extraction steps. Organic phosphorus was considered to be the residual or refractory phosphorus-containing fraction that remained after all other extractions had been performed. 

For example, Legzdins and co-workers (1994) used the bioassay-directed fractionation and chemical analysis technique to isolate, identify, and quantify 2-nitrofluoranthene in extracts of ambient particles collected in Hamilton, Ontario, Canada. They found it accounted for 70% of the total nonpolar direct bacterial mutagenicity (strain YG1021, standard reversion assay, Maron and Ames, 1983). 

Conditions sometimes exist that may make separations by distillation difficult or impractical or may require special techniques. Natural products such as petroleum or products derived from vegetable or animal matter are mixtures of very many chemically unidentified substances. Thermal instability sometimes is a problem. In other cases, vapor-liquid phase equilibria are unfavorable. It is true that distillations have been practiced successfully in some natural product industries, notably petroleum, long before a scientific basis was established, but the designs based on empirical rules are being improved by modern calculation techniques. Even unfavorable vapor-liquid equilibria sometimes can be ameliorated by changes of operating conditions or by chemical additives. Still, it must be recognized that there may be superior separation techniques in some cases, for instance, crystallization, liquid-liquid extraction, supercritical extraction, foam fractionation, dialysis, reverse osmosis, membrane separation, and others. The special distillations exemplified in this section are petroleum, azeotropic, extractive, and molecular distillations. 

There is, on occasion, and depending on the circumstances, the need to analyze the extracts that have been retrieved from coal by the use of various solvents. This assumes that sufficient material has been isolated to proceed with the analysis. The caveat is, of course, that all of the solvent used from the extraction procedure has been removed from the extracts. If not, it may be removed by the use of fractionation techniques applied to the extracts, and corrections will need to be applied to determine the correct yield of the extract fractions. To fractionate the extracts into a variety of subfractions, the nature of the coal must be taken into account as well as the nature of the chemicals extracted from the coal. 

One important trend in the food industry is the increased demand for natural food ingredients free of chemicals. Therefore, special attention has been paid to alternative processes directed toward extraction solvents and techniques with both GRAS and GMP labels (Ibanez et al., 1999). Supercritical C02-extraction (SFC C02) has been used (Weinreich, 1989 Nguyen et al., 1991 Nguyen et al., 1994 Ibanez et al., 1999). Tena et al. (1997) noted that extracts from rosemary obtained by SFC C02 (35 bar at 100°C) were the cleanest extracts and provided the highest recovery of carnosic acid compared to solvent extracts (acetone, hexane, dichlor-methane and methanol) after bleaching with active carbon. Bicchi et al. (2000) reported a fractionated SFC C02 method to selectively isolate carnosol and carnosic acid at 250 atm and 60°C in the second fraction. The authors used 5% methanol to modify the dissolution power of SFC C02. 

Using common extraction procedures and chemical degradation techniques as described above the extractable and nonextractable fraction of four sediment samples of the Teltow Canal were investigated. The extracts as well as the degradation products were analysed by means of gas chromatographic - mass spectrometric analyses. 

Often direct analysis of the sample provides limited information, as a deposit usually contains a multimde of chemical components. For a more detailed analysis it is necessary to separate the components from each other before each component/ fraction is analysed and successive extraction with different solvents (e.g. first ethanol, then ethyl acetate and finally trichloro ethane) will provide additional information over extraction with one solvent only. Other fractionation techniques are available. 

In order to identify compounds responsible for specific effects (i.e., endocrine disrupting or AhR hgands) observed in field studies, TIE or bioassay directed analysis approaches have increasingly been apphed over the last decade. In such approaches, sensitive bioassays are used to direct the fractionation of a sample extract until its complexity is sufficiently reduced to enable identification of those compoimds responsible for the activity measured in the bioassay. This strategy is based on differential extraction and fractionation methods and identification by chemical and biochemical analysis. TIE is a well-established technique having been originally developed by... 

They constitute 75% w/w of the organic matter in most soils and 50% of the organic carbon in surface waters. Humic substances are composed of complex heterogeneous mixtures of organic compounds and are characterized as being yellow to brown in color, of high relative molecular mass, and refractory. Unlike many other natural organic products, they cannot be described in terms of unique chemical structures and are operationally defined by the technique used for their extraction and fractionation. 

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