Unsaturated fatty acid mobilization

The separation of unsaturated fatty acids by HPLC and by CZE has been compared, with applications for such separations in food research and in cancer research.72 A mobile phase containing naphthalene disulfonate,... 

Capillary SFC can be used to analyze triglycerides which contain unsaturated fatty acid groups that are susceptible to degradation. Figure 1 shows the analysis of a soybean oil sample on a 10 m SB-Methyl-100 column using CO2 as the mobile phase at 200 C with an FID. Identification of the compounds was achieved by comparing the retention times of sample components with standard compounds. 

The same authors (59) also noted that changes in mobile phase composition were found to substantially affect the elution order and resolution (Fig. 3.4) of the cis/trans CLA isomers (8t,10c-, 9c, t-, 10t,12c- and llc,13t-18 2). The elution order of the p-methoxyphenacyl derivatives using the hexane/dichloromethane/ACN solvent system was identical to that observed for CLAME with hexane/ACN (llc,13/-, 10/,12c-, 9c,ll/-, then 8/,10c-18 2), but dichloromethane/ACN or hexane/dichloromethane/iso-propanol as solvent resulted in an elution order of 10/,12c-, llc,13/-, 8/,10c-, then 9c,l 1/-18 2. Momchilova and Nikolova-Damyanova also studied the effects of mobile phase composition (61) and of FA chain-length vs. double-bond position (62) for the p-methoxyphenacyl derivatives of unsaturated fatty acids. 

Momchilova, S., and Nikolova-Damyanova, B. (2000) Silver Ion HPLC of p-Methoxyphenacyl Derivatives of Unsaturated Fatty Acids. I. Mobile Phase Effects, J. Liq. Chromatogr. Relcu. Technol. 23, 2303-2316. 

Waldi [181] has separated the esters on silica gel G, using carbon tetrachloride-chloroform (95 + 5). Kauemann et al. [96] have used either tetraUn-hexane (25 + 75) or (50 + 50) for adsorption TLC or paraffin/methyl ethyl ketone-acetonitrile (70 + 30) as reversed phase partition system. All the esters from acetate to stearate yield thus a series of spots like a string of beads. Acetic acid is also a suitable mobile phase, as in PC [125]. Unsaturated fatty acid esters can be differentiated from the saturated esters only with difficulty in this way success is more likely when an adsorption chromatographic separation is carried out... 

The TG fatty acid composition within a plant species depends on the environment, especially the temperature. A general rule is that plants in cold climates produce a higher proportion of unsaturated fatty acids. Obviously, the mobility of TGs is thus retained. In the sunflower (cf. Fig. 3.10), this rule is highly pronounced whereas in safflower, only a weak response to temperature variations is observed (Fig. 3.10). 

The technique involves partition of a solute between a stationary and a mobile phase as in GC, except that in the former both phases are liquids the term "reversed-phase" implies that the mobile phase is more polar than the stationary one. By far the most widely used stationary phase consists of octadecylsilyl C Cie" or "ODS") groups, linked to a silanol surface by covalent bonds, although Cs phases are increasingly being found to have some utility. Invariably, unsaturated fatty acids are eluted appreciably ahead of the saturated fatty acids of the same chain-length, each double bond reducing the retention time (or volume) by the equivalent of about two carbon atoms. Thus oleic acid derivatives tend to elute in the same region as palmitate as these are always major components of plant and animal... 

A great deal of work has been done on the separation of hydroperoxides of unsaturated fatty acids by HPLC and columns of silica gel (reviewed by the author [168]). As the separation is carried out anaerobically at room temperature, little harm can come to the samples. Conjugated double bonds usually present in such fatty acids permit sensitive and specific detection by UV spectrophotometry at 235 nm. The technique has been used with other oxygenated fatty acids, and as an example, epoxy fatty acids were isolated from the total fatty acids of a seed oil by HPLC with a column of Partisir silica gel with hexane-diethyl ether (9 1, v/v) as the mobile phase [871],... 

We have carried out a series of experiments In which the lipid composition of the photosynthetic membrane has been altered by the homogeneous catalytic hydrogenation of the unsaturated fatty acid residues of membrane lipids. Ordering state of lipids was not a linear function of the degree of unsaturation. Decrease of the double bonds beyond about 75% resulted only In a measurable Increase of the orientational order. Progressive saturation of double bonds primarily Inhibited electron transport between the photosystems, followed by the Inhibition of electron flow around PS II. Our results underlined the functional Importance of the presence of polyunsaturated fatty acyl chains, but the hypothesis, that the level of mlcrovlscoslty in the hydrophobic core regulates the electron flow via controlling the rate of diffusion of mobile electron carriers has not been confirmed experimentally. 

If only saturated fatty acids are present, stiff and rigid cell membranes or skin lipids are formed. In contrast to this, phosphohpids and ceramides with a high content of unsaturated fatty acids, such as linoleic acid or GLA, form stmctures which are more mobile and flexible. The result is an increase in the elastidly of the skin since unsaturated fatty acids are incorporated in the cell membranes of the skin. PUFA-nourished skin looks younger and smoother. 

Figure D1.6.3 TLC-FID separation of a range of standard lipids. The mobile phase was 91 6 3 1 (v/v/v/v) hexane/ethyl acetate/diethyl ether/formic acid. Time refers to scanning time of the Chromarod. Abbreviations CE, cholesterol ester CHO, cholesterol DG, 1,2-diglyceride 1,3-DG, 1,3-diglyceride FFAU, highly unsaturated free fatty acid FFAS, less unsaturated free fatty acid MG, 1-monoglyceride PL, phosphatidylcholine TGU, highly unsaturated triglyceride TGS, saturated triglyceride. Tripalmitin and palmitic acid were used to complement trilinolenin and linolenic acid. Reproduced from Ackman and Heras (1997) with permission from AOCS Press.

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