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Improved separation of conjugated fatty acid methyl esters by silver ion‐high‐performance liquid chromatography
Author(s) -
Sehat Najibullah,
Rickert Rainer,
Mossoba Magdi M.,
Kramer John K. G.,
Yurawecz Martin P.,
Roach John A. G.,
Adlof Richard O.,
Morehouse Kim M.,
Fritsche Jan,
Eulitz Klaus D.,
Steinhart Hans,
Ku Yuoh
Publication year - 1999
Publication title -
lipids
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.601
H-Index - 120
eISSN - 1558-9307
pISSN - 0024-4201
DOI - 10.1007/s11745-999-0379-3
Subject(s) - chemistry , high performance liquid chromatography , cis–trans isomerism , isomerization , chromatography , conjugated linoleic acid , elution , resolution (logic) , structural isomer , conjugated system , double bond , fatty acid , linoleic acid , organic chemistry , catalysis , polymer , artificial intelligence , computer science
Operating from one to six silver ion‐high‐performance liquid chromatography (Ag + ‐HPLC) columns in series progressively improved the resolution of the methyl esters of conjugated linoleic acid (CLA) isomeric mixtures from natural and commercial products. In natural products, the 8 trans , 10 cis ‐octadecadienoic (18∶2) acid was resolved from the more abundant 7 trans , 9 cis ‐18∶2, and the 10 trans , 12 cis ‐18∶2 was separated from the major 9 cis , 11 trans ‐18∶2 peak. In addition, both 11 trans , 13 cis ‐18∶2 and 11 cis , 13 trans ‐18∶2 isomers were found in natural products and were separated; the presence of the latter, 11 cis , 13 trans ‐18∶2, was established in commercial CLA preparations. Three Ag + ‐HPLC columns in series appeared to be the best compromise to obtain satisfactory resolution of most CLA isomers found in natural products. A single Ag + ‐HPLC column in series with one of several normal‐phase columns did not improve the resolution of CLA isomers as compared to that of the former alone. The 20∶2 conjugated fatty acid isomers 11 cis , 13 trans ‐20∶2 and 12 trans , 14 cis ‐20∶2, which were synthesized by alkali isomerization from 11 cis , 14 cis ‐20∶2, eluted in the same region of the Ag + ‐HPLC chromatogram just before the corresponding geometric CLA isomers. Therefore, CLA isomers will require isolation based on chain length prior to Ag + ‐HPLC separation. The positions of conjugated double bonds in 20∶2 and 18∶2 isomers were established by gas chromatography‐electron ionization mass spectrometry as their 4,4‐dimethyloxazoline derivatives. The double‐bond geometry was determined by gas chromatography‐direct deposition‐Fourier transform infrared spectroscopy and by the Ag + ‐HPLC relative elution order.