Lipids

, Volume 34, Issue 8, pp 873–877

Preparation, separation, and confirmation of the eight geometrical cis/trans conjugated linoleic acid isomers 8,10-through 11,13–18∶2

Authors

  • Klaus Eulitz
    • Centerfor Food Safety and Applied NutritionUS Food and Drug Administration
    • Centerfor Food Safety and Applied NutritionUS Food and Drug Administration
  • Najibullah Sehat
    • Centerfor Food Safety and Applied NutritionUS Food and Drug Administration
  • Jan Fritsche
    • Centerfor Food Safety and Applied NutritionUS Food and Drug Administration
  • John A. G. Roach
    • Centerfor Food Safety and Applied NutritionUS Food and Drug Administration
  • Magdi M. Mossoba
    • Centerfor Food Safety and Applied NutritionUS Food and Drug Administration
  • John K. G. Kramer
    • Southern Crop Protection, Food Research CenterAgriculture and Agri-Food Canada
  • Richard O. Adlof
    • Northern Regional Research Center, ARSUSDA
  • Yuoh Ku
    • Centerfor Food Safety and Applied NutritionUS Food and Drug Administration
Article

DOI: 10.1007/s11745-999-0435-z

Cite this article as:
Eulitz, K., Yurawecz, M.P., Sehat, N. et al. Lipids (1999) 34: 873. doi:10.1007/s11745-999-0435-z

Abstract

Conjugated linoleic acid (CLA) mixtures were isomerized with p-toluenesulfinic acid or I2 catalyst. The resultant mixtures of the eight cis/trans geometric isomers of 8,10-, 9,11-, 10,12-, and 11,13-octadecadienoic (18∶2) acid methyl esters were separated by silver ion-high-performance liquid chromatography (Ag+-HPLC) and gas chromatography (GC). Ag+-HPLC allowed the separation of all positional CLA isomers and geometric cis/trans CLA isomers except 10,12–18∶2. However, one of the 8,10 isomers (8cis, 10trans-18∶2) coeluted with the 9trans,11cis18∶2 isomer. There were differences in the elution order of the pairs of geometric CLA isomers resolved by Ag+-HPLC. For the 8,10 and 9,11 CLA isomers, cis,trans eluted before trans,cis, whereas the opposite elution pattern was observed for the 11,13–18∶2 geometric isomers (trans,cis before cis,trans). All eight cis/trans CLA isomers were separated by GC on long polar capillary columns only when their relative concentrations were about equal. Large differences in the relative concentration of the CLA isomers found in natural products obscured the resolution and identification of a number of minor CLA isomers. In such cases, GC-mass spectrometry of the dimethyloxazoline derivatives was used to identify and confirm coeluting CLA isomers. For the same positional isomer, the cis,trans consistently eluted before the trans,cis CLA isomers by GC. High resolution mass spectrometry (MS) selected ion recording (SIR) of the molecular ions of the 18∶1 18∶2, and 18∶3 fatty acid methyl esters served as an independent and highly sensitive method to confirm CLA methyl ester peak assignments in GC chromatograms obtained from food samples by flame-ionization detection. The high-resolution MS data were used to correct for the nonselectivity of the flame-ionization detector.

Abbreviations

Ag-HPLC

silver ion-high-performance liquid chromatography

cis/trans

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

CLA

conjugated linoleic acid

DMOX

4,4-dimethyloxazoline

FAME

fatty acid methyl esters

FID

flame-ionization detector

GC-EIMS

gas chromatography-electron ionization mass spectrometry

SIR

selected ion recording

UV

ultraviolet

Copyright information

© AOCS Press 1999