In lipid extraction

Chloroform-methanol extracts of Borrelia burgdorferi were used for the identification of lipids and other related components that could help in the diagnosis of Lyme disease [58]. The provitamin D fraction of skin lipids of rats was purified by PTLC and further analyzed by UV, HPLC, GLC, and GC-MS. MS results indicated that this fraction contained a small amount of cholesterol, lathosterol, and two other unknown sterols in addition to 7-dehydrocholesterol [12]. Two fluorescent lipids extracted from bovine brain white matter were isolated by two-step PTLC using silica gel G plates [59]. PTLC has been used for the separation of sterols, free fatty acids, triacylglycerols, and sterol esters in lipids extracted from the pathogenic fungus Fusarium culmorum [60]. 

F.O. Giilagar, A. Buchs, A. Susini, Capillary gas chromatography mass spectrometry and identification of substituted carboxylic acids in lipids extracted from a 4000 year old Nubian burial, Journal of Chromatography, 479, 61 72 (1989). 

The observation of high levels of free sialic acid in lipid extracts of WgaKI1 and WgaRVIII cells prompted us to examine whether it might be sialic acid complexed with the nucleotide cy-tidine monophosphate (i.e. CMP-sialic acid). 

Other extraction methods used in the lipid extraction include supercritical fluid extraction (SFE) and pressurized liquid extraction (PLE). With SEE, good extraction yields have been obtained for nonpolar lipids including ester-ified fatty acids, acylglycerols, and unsaponifiable matter. However, complex polar lipids are only sparingly soluble in supercritical carbon dioxide alone and polar modifiers, such as methanol, ethanol, or even water is required to improve the extraction of polar lipids (10). SFE has been used for the extraction of lipids especially from various food matrices, such as different nuts, edible oils, and seeds (11). The recoveries of lipids in SFE were on the same levels than with conventional solvent extraction methods (12,13), no significant differences between the fatty acids extracted were observed. PLE has also been used in lipid extraction, although only in very few applications (14). The elevated temperatures used in PLE can cause alteration of the lipid composition. 

A number of workers have observed amino acids in lipide extracts, including those of microbial origin (11, 12, 17, 29). Recently, Macfar-lane (34) has reported that most of the phospholipide in Clostridium welchii is bound to amino acids and that some of this material occurs as the O-amino acid ester of phosphatidylglycerol. The relatively prominent occurrence of lipides in cell membranes has led to the recurrent suggestion that transport of hydrophilic substances through such membranes would be greatly facilitated by combination with hydrophobic substances. Consequently, most workers who have observed the incorporation of amino acids into lipide fractions quite naturally... 

At present hydrolysis with alkali or phospholipase D enzyme is used to cleave the As moiety in lipid extracts and the water-soluble As species liberated are analyzed by HPLC-ICP-MS [32, 33, 99]. Lipid-soluble As species such as phosphatidyl AC and phosphatidyl arsenosugar on treatment release DMA, MA, AC, and glycerol arsenosugar. 

Terpenoids occur as essential oils in lipid extractions of plants. 

A2. Antonis, A., The colorimetric determination of ester groups in lipid extracts. J. Lipid Res. 1, 485-486 (1960). 

Fatty acids commonly occur in lipid extracts, where they exist in both free and esterified forms. Free fatty acids are isolated along with the neutral lipids. The esterified fatty acids can be released via hydrolysis of lipids. Negative-ion FAB and ESI are the most suitable modes of ionization for fatty acids. In combination with CID, a wealth of structmal information has been gathered by using these two modes of ionization for fatty acids and other lipid species. Electron ionization (EI)-MS has also been one of the successful mass spectrometric... 

Thomas, M. J., Chen, Q., Sorci-Thomas, M. G., and Rudel, L. L. 2001. Isoprostane levels in lipids extracted from atherosclerotic arteries of nonhuman primates,... 

As chlorinated fatty acids in lipid extracts cannot be separated from non-chlorinated matrix by routine cleanup techniques, because of the similarity in their chemical and physicochemical properties, chromatographic elution is often the sole effective means of separation for identification and quantitation of chlorinated fatty acids. As chlorinated fatty acids are present in biota extracts at trace levels, it is critical to have a detector that is highly specific for... 

The analysis of FAs by GC in their free form is practically restricted to the volatile short chains (less than 10 carbons) present in lipid extracts, such as in milk fat, and cheese samples. For most FA mixtures, the use of ester derivatives, mainly methyl esters, is recommended. These esters are more volatile than the corresponding free FAs and, therefore, more suitable for analysis by GC in the gaseous form. They are also less polar, thereby reducing their adsorption onto the support and dimerization in the vapor phase with subsequent reduction in peak tailing and/ or ghosting, improved peak shape, and resolution. 

Other methods for determining carbonyl compounds involve derivatization followed by column chromatography or by HPLC or by GC. Total carbonyls in lipid extracts are converted to their 2,4-DNPHs by using a column of diatomaceous earth impregnated with 2,4-DNPH, followed by extraction and spectrophotometric measurement at 340 nm. By reaction with methylhydrazine. 

Using TLC, several uncommon sterols have been detected in the aorta, especially that of new-born babies [202]. Methyl esters and, in some cases, aldehyde trimers (1,3,5-trioxans) have also been discovered in lipid extracts of human organs. It is assumed, however, that these compounds were formed from free fatty acids or aldehydes, respectively, during extraction of the tissue and storage of the extracts [202]. 

Up to 20 different lipid classes, some of which have not yet been identified, have been detected in lipid extracts of potatoes [111], wheat endosperms [128], lettuce- and cabbage leaves [150] and spinach leaves [57] by means of two-dimensional TLC on silica gel G. TCL proved to be a useful tool for isolating the phosphatidyl glycerols from spinach leaves [57]. 

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