Quantitative determination of conjugated linoleic acid isomers in beef fat

The amounts of 14 conjugated linoleic acid (CLA) isomers (t12t14, t11t13, t 10t12, t9t11, t8t10, t7t9, t6t8; 12,14 c/t, t11c13, c11t13, t10c12, 9,11 c/ t, t8c10, t7c9-18:2) in 20 beef samples were determined by triple-column si lver-ion high-performance liquid chromatography (Ag+-HPLC). Quantitation wa s performed using an external CLA reference standard consisting of cis9, tr ans11-18:2, trans9, trans11-18:2 and cis9,cis11-18:2. Linearity was checked as being r > 0.9999 between 0.02 x 10(-3) to 2 mg/ml. The determination li mit (5-fold signal/noise ratio) of the CLA reference was estimated to be 0. 25, 0.50, 1.0 ng/injection for the cis/trans, trans,trans and cis,cis isome rs, respectively. As expected, cis9,trans11-18:2 was the predominant isomer (1.95 +/- 0.54 mg/g fat) in beef, followed by trans7,cis9-18:2 (0.19 +/- 0 .04 mg/g fat); cis,cis isomers were below the determination limit in most b eef samples. Total CLA amounts determined by Ag+-HPLC were compared to tota l CLAs determined by gas chromatography (GC, 100 m CPSil(TM) 88 column). Th e amounts obtained by GC were generally higher than those determined by Ag-HPLC due to co-eluting compounds.