Phospholipids solid-phase extraction

Recently, however, prepacked solid-phase extraction (SPE) columns have been preferred. In this case, too, the phospholipid fraction is often recovered by elution with methanol. Thus, Nash and Frankel developed a method to recover the phospholipids from 1-g portions of crude oils using silica gel Sep-Pak cartridges (29). The oil was applied as a 10% solution in a 95/5 (v/v) mixture of petroleum ether and diethyl ether, and neutral lipids (about 94-97%) were eluted with 10 ml of additional solvent the so-called unsaponifiables (2-3%) were recovered using 20 ml of diethyl ether, and the phospholipid fraction was obtained using 10 ml of methanol. 

Actually, solid-phase extraction is used not only as a rough preliminary fractionation procedure. Prieto et al. described the complete fractionation of the total lipids from wheat into eight neutral lipid, two glycolipid, and four phospholipid classes in addition to PC and LPC, TV-acyl PE and A-acyl LPE were detected (37). However, two separate stationary phases (silica and aminopropyl) as well as seven different mobile phases were needed. Moreover, 14% crosscontamination of PC and LPC was observed, and the recovery of the phospholipids was limited to about 85%. Hence, SPE is a rapid and efficient technique for preliminary fractionation, but loses its advantages if more complex separations are tried. 

T Horne, S Holt-Larkin. Solid-phase extraction of phospholipids from hemoglobin solutions using Empore styrene-divinylbenzene disks. J Chromatogr B 695 259-267, 1997. 

Solid phase extraction allows yielding a much cleaner extract than PP, since it significantly lowers phospholipids levels which represent the major endogenous compounds causing significant matrix effects [263-265],... 

Operational equations from our FA model have been used to estimate FA fluxes, turnover rates, and half-lives within brain phospholipids in vivo, after values for the dilution factor X of the acyl-CoA pool were experimentally determined. This can be accomplished by a rapid method involving oligonucleotide solid-phase extraction (Deutsch et al., 1997). Low experimental values for X in the awake rat, between 0.02 and 0.04, are consistent with very short half-lives resulting from de-esterificafion-re-esteri-fication of FAs within some phospholipids (minutes to hours), very rapid turnover rates and high ATP consumption (Purdon Rapoport, 1998). 

Suzuki, E. Sano, A. Kuriki, T. Miki, T. Improved separation and determination of phospholipids in animal tissues employing solid phase extraction. Biol. Pharm. BuU 1997, 20 (4), 299-304. 

The bioactive core aldehydes derived from the oxidation of LDL phospholipids (see Section E.2) can be analysed either directly by LC-MS or after hydrolysis by phospholipases and sodium borohydride reduction. These aldehyde esters are purified by solid-phase extraction followed by preparative TLC. Unwanted ester containing phospholipids can be removed after treatment with phospholipase Al. The more polar oxidized phospholipids are eluted by HPLC after the class of phospholipids from which they are derived. The core aldehydes derived from oxidized phospholipids (Section E.2) are also known to be pro-inflammatory. Only a few C-4 and C-5 core aldehydes have been identified and analysed by LC-MS, either directly or after derivatization in oxidized LDL. Many more saturated and unsaturated core aldehydes can be expected in oxidized LDL, according to the degree and mode of oxidation. However, the abihty of these core aldehydes to form covalent adducts with the apoB of LDL may prevent them from being detected directly by LC-MS. Chemical or enzymatic hydrolysis may therefore be required before they can be analysed by this technique. 

Total phospholipid content of soybean lecithin can be obtained by solid phase extraction on silica. Lipids are eluted with 20 80 hexane/ethyl ether, then phospholipids are eluted with methanol. The amount of each fraction is determined gravimetrically after solvent removal (31). 

For the sake of completeness, it must be mentioned that two additional solid phases were also included in this study (Table 3). However, only 43% and 23% of the PL present in the lipid extract of egg powder were recovered from a C18 and a silica column, respectively (32). Table 3 reveals that the PL recovered from Cu were depleted in the neutral phospholipids PE, PC, and... 

Liquid-liquid extractions (13) permit the elimination of slightly polar molecules (phospholipids, fatty acids, etc) that may interfere in the HPLC determination of carbohydrates. Hence, for solid foodstuffs, some form of extraction will be required prior to the chromatographic procedure, and even in liquid food samples it may be necessary to modify the solvent composition of the liquid phase to make it compatible with the HPLC eluent. The major role of the extracting solvent is to obtain all of the carbohydrate present in the food sample dissolved in a liquid phase, be it for direct injection into the chromatograph or for subsequent cleanup stages prior to HPLC. 

P NMR spectroscopy is a useful tool to discriminate between phosphorylated molecules in liquid or amorphous/solid-like sample with respect to their nature and dynamics. The major advantage of the NMR technique is that the sample can be analysed without pretreatment or extraction, and can be recovered since NMR is non-destructive. Phosphates in milk and in isolated casein micelles have been widely investigated using liquid-state P NMR spectroscopy As the restricted motion induced by the large colloidal structure of casein micelles does not permit the obtaining of hi ly resolved spectra, only the mobile phosphates (a part of easein phosphoprotein residues, the dissociated inorganic phosphate and the milk fat phospholipids) found in the soluble phase were detected by liquid-state NMR. 

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