Lipid, analysis solubility

Figure 7.2 Partial capillary gas chromatogram displaying the principal lipid solvent soluble constituents of a black tarry deposit on the surface of a Neolithic potsherd from Ergolding Fischergasse, Bavaria, Germany. The sample was trimethylsilylated prior to GC (for further details see Heron et al., 1997). Peak identities (confirmed by GC-MS analysis) 1, lupenone 2, lupeol 3, betulin 4, betulinic acid.

Solid-phase microextraction (SPME), volatile lipid analysis, 534-535 Solubility, protein hydration properties, 295 (table)... 

Irradiation of the lipid (fet soluble) phase of a meat extract does not produce the characteristic off-odor while irradiation of the aqueous (water soluble) portion of die meat extract results in a typical irradiation odor (20). 3) Irradiation of sulfur-containing amino acids or polypeptides produced a similar off-odor as the irradiation odor (21). 4) The amount of VSCs increased with radiation dose while volatiles from lipids were not always correlated with radiation dose (19). Several earlier researchers suggested that hydrogen sulfide (H2S) and methanethiol (MT) were important for the development of the off-odor (12, 20, 22). Patterson and Stevenson (23), using GC-olfactory analysis, showed that dimethyl trisulfide (DMTS) was the most potent off-odor compound in irradiated raw chicken meats followed by cis-3- and trans-6-nonenals, oct-l-en-3-one and bis(methylthio-)methane. Aim and his colleagues have published extensively on irradiation-induced volatile compounds in raw meats (11). They have identified MT, dimethyl sulfide (DMS), dimethyl disulfide (DMDS) and DMTS in different types of irradiated raw meats using GC-FID and GC-MS. 

All lipid analyses are preceded by isolation of the total lipid material by solvent extraction with a solvent such as CHCI3. As far as seawater and the microlayer are concerned it cannot be stressed too strongly that this method of isolation specifically excludes water-soluble organic compounds from whatever form of organic analysis that follows. The lipid extract is normally then hydrolysed with aqueous acid or base which breaks the ester linkages, releasing the constituents of the combined lipids. Water-soluble components such as glycerol and the phosphoric acid of phospholipids are removed... 

Figure 50 shows the potential fo packed-column SFC for an efficient and fast control of the chiral purity of pharmaceuticals. Because of the excellent solubility of lipids in supercritical carbon dioxide, SFC in combination with the universal FID detector is a very helpful tool in lipid analysis. 

Multiple new developments related to the different components of mass spectrometers (e.g., ion source and analyzer) have been made in the last several years. For example, atmospheric-pressure photoionization (APPI) has become the newest family member of atmospheric-pressure ionization (API) techniques in addition to ESI and APCI. APPI has provided a new approach to analyze compounds notreadily ionized by ESI with improved ionization efficiency in comparison to APCI. Therefore, APPI serves as a complementary alternative to ESI for lipid analysis. Since APPI requires less heat for desolvation than APCI, thermally labile compounds can be analyzed with fewer concerns for thermal chemical alterations or degradation in the ionization source. In addition, APPI offers lower detection limits, higher signal intensities, and higher signal to noise ratios in comparison to APCI. Therefore, APPI has been well-appreciated for its ability to analyze many neutral lipid classes, including free fatty acids (and their esters), MG, DG, TG, sterols, fat-soluble vitamins, and even polar phospholipids. 

Gel permeation ehromatography (GPC)/normal-phase HPLC was used by Brown-Thomas et al. (35) to determine fat-soluble vitamins in standard referenee material (SRM) samples of a fortified eoeonut oil (SRM 1563) and a eod liver oil (SRM 1588). The on-line GPC/normal-phase proeedure eliminated the long and laborious extraetion proeedure of isolating vitamins from the oil matrix. In faet, the GPC step permits the elimination of the lipid materials prior to the HPLC analysis. The HPLC eolumns used for the vitamin determinations were a 10 p.m polystyrene/divinylbenzene gel eolumn and a semipreparative aminoeyano eolumn, with hexane, methylene ehloride and methyl tert-butyl ether being employed as solvent. 

Selected applications of coupled SEE-SEC consider the analysis of tocopherols in plants and oil by-products (65) or the analysis of lipid-soluble vitamins (66) by using a dynamic on-line SEE-SEC coupling, integrated in the SE chromatograph, based on the use of micropacked columns. 

Quinones, lipid-soluble substances involved in electron transport, can also be used as biomarkers. Lipski et al. (155) u.sed quinone analyses, physiological tests, and fatty acid profiles to differentiate Gram-negative non-fermentative bacteria isolated from biofilters. Quinone type was found to be an efficient method to group isolates prior to the analysis of results from the physiological tests. The detection of quinones appears to be restricted to the discrimination of isolated colonies and has limited potential to the analysis of mixed populations. 

The use of SPE with porous materials such as alumina, diatomaceous earth, Horisil and silica for the cleanup of fat-soluble organochlorine pesticides in fatty foods such as meat, flsh, shellfish, milk and vegetable oils has been well documented. The choice of elution solvents is critical because relatively small amounts of lipid in the final extract can cause rapid deterioration of GC capillary columns and also contaminate the gas chromatograph. A number of workers have used a porous material in tandem with Cig to effect an improved cleanup.Di Mucchio employed a multicartridge system comprising Extrelut, silica and Cig to extract organophosphorus pesticides from oils and fatty extracts. Relatively few literature applications include the pyrethroids, but Ramesh and Balasubramanian reported a simple carbon-based SPE method for the analysis of pyrethroids in vegetable oil. 

New insights into the analysis of hydrophobically post-translational modified proteins could be achieved by the construction of lipidated proteins in a combination of bioorganic synthesis of activated lipopeptides and bacterial expression of the protein backbone (Fig. 19). The physico-chemical properties of such artificial lipoproteins differ substantially from those of the corresponding lipopeptides. The pronounced dominance of the hydrophilic protein moiety (e.g., for the Ras protein 181 amino acids) over a short lipopeptide with one or two hydrophobic modifications provides solubility up to 10 4 mol/1, while the biotinylated or fluorescence labeled lipopeptides exhibit low solubility in aqueous solutions and can be applied in the biophysical experiments only in vesicle integrated form or dissolved in organic solvent. 

Fenthion has also exhibited delayed neurotoxicity in which the initial cholinergic crisis was delayed 5 days and recurred 24 days after ingestion. Psychosis was a persistent manifestation. Because of the high lipid solubility of fenthion, toxin analysis of repeated fat biopsies was an essential component of patient management. ... 

Lipids with a suitable hydrophilic-lipophilic balance (HLB) are known to spread on the surface of water to form monolayer films. It is obvious that if the lipid-like molecule is highly soluble in water, it will disappear into the bulk phase (as observed for SDS). Thus, the criteria for a monolayer formation are that it exhibits very low solubility in water. The alkyl part of the lipid points away from the water surface. The polar group is attracted to the water molecules and is inside this phase at the surface. This means that the solid crystal, when placed on the surface of water, is in equilibrium with the him spread on the surface. A detailed analysis of this equilibrium has been given in the literature (Gaines, 1966 Adamson and Gast, 1997 Birdi, 2009). The thermodynamics allows one to obtain extensive physical data on this system. It is thus apparent that, by studying only one monolayer of the substance, the effect of temperature can be very evident. 

Retinoids The challenge in fat-soluble vitamins analysis is to separate them from the lipid fraction that contains interferents. Alkaline hydrolysis, followed by LLE, is widely applied to remove triglycerides. This technique converts the vitamin A ester to all-trani-retinol. A milder process, which does not hydrolyze vitamin A ester, is alcoholysis carried out with metha-nolic KOH solution under specific conditions that favor alcoholysis rather than saponification. A more accurate explanation of this technique is reported in the book Food Analysis by FIPLC [409]. For some kind of matrices a simple liquid extraction can be sufficient with [421-423] or without [424,425] the purification... 

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