Relative retention order of all isomers of cis/trans conjugated linoleic acid FAME from the 6,8‐ to 13,15‐positions using silver ion HPLC with two elution systems

CLA, defined as one or more octadecadienoic acids (18∶2) with conjugated double bonds, has been reported to be active in a number of bological systems. GC and silver ion HPLC (Ag + ‐HPLC) have been the primary techniques for identifying specific CLA isomers in both foods and biological extracts. Recently, GC relative retention times were reported for all c,c, c/t ( c,t and t,c ), and t,t CLA FAME from the 6,8‐ to the 13,15‐positions in octadecadienoic acid (18∶2). Presented here is the relative retention order of the same CLA FAME using Ag + ‐HPLC with two different elution systems. The first elution system, consisting of 0.1% acetonitrile/0.5% diethyl ether (DE)/hexane, has been used previously to monitor CLA composition in foods. Also presented here is the retention order of CLA FAME using 2% acetic acid/hexane elution solvent, which has advantages of more stable retention volumes and a complementary elution order of CLA FAME isomers. The data are reported using retention volumes (RV) adjusted for toluene, an estimator for dead volume, and relative to c 9, t 11‐18∶2. Measurement of relative RV in the analysis of 88 samples of cow plasma, milk, and rumen fluids using Ag + ‐HPLC is also presented here. The % CV ranged from 1.04 to 1.62 for t,t isomers and from 0 to 0.48 for c/t isomers.