Enhanced resolution of conjugated linoleic acid isomers by tandem-column silver-ion high performance liquid chromatography

A commercial mixture of conjugated linoleic acid (CLA) isomers, reportedly consisting of six components, was recently resolved into 12 peaks attribute d to CLA isomers using silver-ion high performance liquid chromatography (A g+-HPLC). In this study, the coupling of two analytical silver-ion high per formance liquid chromatography columns (tandem-column Ag+-HPLC) in series l ed to the enhanced resolution of CLA isomers, Many CLA isomers mere baselin e resolved and the pair 18:2 8,10 c/t and 18:2 7,9 c/t found in cheese prod ucts, was resolved for the first time, In this work, a similar commercial C LA mixture was separated into 16 peaks, while CLA isomers from cheese also gave rise to 16 peaks, As expected, the CLA isomers were separated into thr ee geometric groups in the order trans,trans, cis/trans, and cis,cis. Semi- preparative Ag+-HPLC, followed by gas chromatography-mass spectroscopy of t he dimethyloxazoline derivatives, was used to confirm the identity of the n ewly resolved positional CLA isomers. The double bond configuration of CLA isomers was established by gas chromatography-Fourier transform infrared sp ectroscopy, Tw minor t,t CLA isomers found in cheese, presumably 18:2 t6t8 and 18:2 t13t15, mere also separated. The CLA isomeric composition of 16 co mmercial cheese products was determined.