Lipids

, Volume 34, Issue 4, pp 407–413 | Cite as

Improved separation of conjugated fatty acid methyl esters by silver ion-high-performance liquid chromatography

  • Najibullah Sehat
  • Rainer Rickert
  • Magdi M. Mossoba
  • John K. G. Kramer
  • Martin P. Yurawecz
  • John A. G. Roach
  • Richard O. Adlof
  • Kim M. Morehouse
  • Jan Fritsche
  • Klaus D. Eulitz
  • Hans Steinhart
  • Yuoh Ku
Method

Abstract

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.

Abbreviations

CFA

conjugated fatty acids

cis/trans

refers to all the CLA isomers having either a cis, trans or a trans, cis configuration

CLA

conjugated linoleic acid

DMOX

4,4-dimethyloxazoline

FAME

fatty acid methyl esters

GC-DD-FTIR

gas chromatography-electron ionization mass spectrometry

Ag+-HPLC

silver ion-high-performance liquid chromatography

PUFA

polynsaturated fatty acids

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Copyright information

© AOCS Press 1999

Authors and Affiliations

  • Najibullah Sehat
    • 1
  • Rainer Rickert
    • 2
  • Magdi M. Mossoba
    • 1
  • John K. G. Kramer
    • 3
  • Martin P. Yurawecz
    • 1
  • John A. G. Roach
    • 1
  • Richard O. Adlof
    • 4
  • Kim M. Morehouse
    • 1
  • Jan Fritsche
    • 1
  • Klaus D. Eulitz
    • 1
  • Hans Steinhart
    • 2
  • Yuoh Ku
    • 1
  1. 1.U.S. Food and Drug AdministrationCenter for Food Safety and Applied NutritionWashington, DC
  2. 2.Institute of Food ChemistryUniversity of HamburgHamburgGermany
  3. 3.Southern Crop Protection, Food Research CenterAgriculture and Agri-Food CanadaGuelphCanada
  4. 4.USDA-ARS-NCAURPeoria
  5. 5.Office of Food Labeling, HFS-175U.S. Food and Drug AdministrationWashington DC

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