Compound class fractionation method

No class reaction has been proposed for the measurement of total sterols. Instead, various fractionation methods, usually derived from the biochemical litreature, have been adapted to the concentrated materials collected from seawater. Certain of the more important sterols, particularly those used in the evaluation of water quality, have been determined by the use of a compound-specific reaction, after concentration from solution. Thus Wann et al. [405,... 

In this paper we outline techniques used to isolate two specific classes of compounds as well as a general class separation method suitable for large scale production of fractions. The specific isolation schemes are devised to produce an alkane or a PAH-enriched fraction. The general scheme provides for rapid fractionation of whole samples into several broad chemical classes. 

Methods of analysis by direct injection in the column of sample were proposed (Lea et al., 1979 Nagel et al., 1979 Ong and Nagel, 1978 Wulf and Nagel, 1976 Roggero et al., 1989 Lamuela-Raventos and Waterhouse, 1994), but usually, prior to analysis, the different classes of compounds are fractionated on absorbent polymers such as polyamide, Sephadex LH20 or C18. The stationary phase C18 is also used for concentration and purification of the sample by solid phase extraction (SPE) prior to analysis. 

Some of the substances that have been separated by this method are given in papers referred to by Morris and Morris (1964) amino acids, peptides (particularly those having molecular weights ranging from 500 to 5000), polypeptide antibiotics, proteins (including enzymes), carbohydrates (although for most compounds in this chemical class other fractionation methods are much more frequently applied), purines, pyrimidines, nucleic acid derivatives, tRNA s that are specific for various amino acids, organic acids, steroids, lipids, antibiotics that are not peptides, porphyrins, pterins, vitamin B,2 and other vitamins, lipoic acid, and alkaloids. The countercurrent-distribution procedure of Holley et al. (1965) is widely used, sometimes with modifications. Korte et al. (1965) have separated three isomers of tetrahydrocannabinol. 

This method can be employed for fractionating lipids according to compound classes (see p. 408 and 414) it has found greater application, however, for separating mixtures of vinylogous and homologous substances... 

The latroscan TLC/FID MK-5 commercial apparatus is shown in Figure 8.7 Recent applications of rod TLC/FID include a quantitative method for compound class characterization of coal-tar pitch without previous fractionation (Ceb-oUa et al., 1996) analysis of four oil and condensate samples (Kabir et al., 1997) determination of polar lipids in spinach, flagellate, and dinoflagellate samples (Parrish et al., 1996) and analysis of mixtures of triglycerides and oleic acid (Peyrou et al., 1996). 

Conversion (upgrading) of bitumen and heavy oils to distillate products requires reduction of the MW and boiling point of the components of the feedstocks. The chemistry of this transformation to lighter products is extremely complex, partly because the petroleum feedstocks are complicated mixtures of hydrocarbons, consisting of 10 to 10 different molecules. Any structural information regarding the chemical nature of these materials would help to understand the chemistry of the process and, hence, it would be possible to improve process yields and product quality. However, because of the complexity of the mixture, the characterization of entire petroleum feedstocks and products is difficult, if not impossible. One way to simpHfy this molecular variety is to separate the feedstocks and products into different fractions (classes of components) by distillation, solubility/insolubility, and adsorption/desorption techniques. For bitumen and heavy oils, there are a number of methods that have been developed based on solubility and adsorption. The most common standard method used in the petroleum industry for separation of heavy oils into compound classes is SARA (saturates, aromatics, resins, and asphaltenes) analysis. Typical SARA analyses and properties for Athabasca and Cold Lake bitumens, achieved using a modified SARA method, are shown in Table 1. For comparison, SARA analysis of Athabasca bitumen by the standard ASTM method is also shown in this table. The discrepancy in the results between the standard and modified ASTM methods is a result of the aromatics being eluted with a... 

Analytical methods such as thin layer chromatography with flame ionization detection (TLC-FID) (Karlsen barter, 1991) are widely used in the oil industry. These solubdity based separation methods allow for the investigation of crude oil components based on polarity. However they can yield very different amounts of Saturates, Aromatics, Resins and Asphaltenes (SARA) depending on the nature of solvents used in the sepraration. At a p>anel discussion on standardization of petroleum fractions held at the 2009 Petrophase conference, a need to unify and improve the separation methods for asphaltenes and resins was expressed (Merino-Garcia et al., 2010). The diversity of operating definitions employed and measurement variability affect the ability of researchers to determine whether compound classes are present and to draw cross-comp>arisons among measurements from different... 

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