Isolation and characterization of dinners formed in used soybean oil

Dimers were isolated from two samples of partially hydrogenated soybean oil which had been used for frying. They were then separated into their component structures using an LC‐18 octadecyl bonded, HPLC column with acetone‐acetonitrile (1:1, v/v) as the mobile phase with refractometry as the mode of detection and identified by gas chromatography‐mass spectrometry. Evidence is presented for the presence of the monohydroxy, dihydroxy, and keto groups in the dimer of linoleic acid as well as the dehydrodimer, the bicyclic, the tricyclic, and the thermal dimer of methyl linoleate and the dehydrodimer of methyl oleate.