Methyl linoleates, retention times

Figure C4.2.4 (A) SP-HPLC of methyl hydroxyoctadecadienoates obtained from linoleic acid hydroperoxide products. Peak 1, methyl 13-hydroxy-9(Z),11( )-octadecadienoate peak 2, methyl 13-hydroxy-9( ),11(E)-octadecadienoate peak 3, methyl 9-hydroxy-10(E),12(Z)-octadecadi-enoate peak 4, methyl 9-hydroxy-10( ),12( )-octadecadienoate. In this chromatogram, peaks 2 and 4 are more abundant than ordinarily encountered retention times may vary (but not the order of elution) depending on the type of silica HPLC column. (B) CP-HPLC of peak 1 from A. The 13(R)-stereoisomer elutes before the 13(S)-stereoisomer. Elution times may vary. (C) CP-HPLC of peak 3 from A. The 9(S)-stereoisomer elutes before the 9(R)-stereoisomer. Elution times may vary.

Acetonitrile was used in the mobile phase when ultraviolet detection of the carbonyl group at 205 nm was used for the various dimers. Separation of the thermal dimer of methyl linoleate and the dehydrodimer of methyl oleate was again incomplete. The sample at concentrations as low as those required for UV detection (1-5 mg/ml) was sparingly soluble in the mobile phase, resulting in increased retention times. Finally, incomplete separation was obtained when various systems of acetonitrile/methyl chloride were used as the mobile phase in HPLC with infrared detection of the carbonyl group at 5.72 /xm. 

The ester compositions of the JCME are given in Table 3. Three main fatty acid esters were identified in the biodiesel fuel, namely the methyl esters of palmitic acid (17%), oleic acid (17%) and linoleic acid (43%). The biodiesel also showed an unknown peak with retention time of 79.5 minutes. Other components were as described in the literature, although the relative amounts differed. ... 

The methyl ester of the 9-hydroxy linoleate has adjusted retention times of 65.5 and 55.3 min on a particular column at temperatures of 200 and 215°C, respectively. Will it be possible to elute this compound in less than 40 min, if the liquid phase in the column has a maximum operating temperature of 240°C ... 

The presence of conjugated double bond systems in the alkyl chain increases the retention time of an ester considerably over that of a similar compound with methylene-interrupted double bonds. Methyl 9-c/s,11-frans-octadecadienoate, for example, is a common minor constituent of ruminant and other tissues and has ECL values of 20.48 on EGSS-X and 20.24 on EGSS-Y , i.e. appreciably greater than the corresponding values for methyl linoleate [161]. In addition, the configuration of the double... 

Relative Retention Times (RRT) of Conjugated Linoleic Acid (CLA) Methyl Ester Isomers on a 100-m... 

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