DIRECT DETERMINATION OF TRANS-OCTADECENOIC ACID IN DIET COMPOSITES USING A COMBINATION OF SILVER ION HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHYAND CAPILLARY GAS-CHROMATOGRAPHY

Silver ion-high performance liquid chromatography (Ag-HPLC) and capill ary gas chromatography (GC) were combined to quantify, total trans-oct adecenoic acid (18:1t) in diet composites and oils. The 18:1 cis and t rans fatty acid methyl esters (FAME) of saponified and methylated (BF3 /methanol) oils and food composite total lipid extracts were separated by Ag-HPLC (ChromSpher5 Lipids column); total 18:lt in the trans frac tion was quantified by GC (105m x 0.25mm SP-2560 capillary column). Po sitional isomers 18:le and 18:lt which coeluted in direct GC were clea rly separated by preparatory Ag-HPLC. Quantitative recovery of 18: It from a standard mixture of FAME, an oil, and a diet composite was obta ined for additions of 4-57 mg The analytical range for total 18: It wa s 1.6-260 mg/mL per aliquot of total lipid extract or oil. Relative st andard deviations were <6% for food composites and <3% for oils and pu re standards.