Gas chromatographic separation of docosenoic acid positional isomers on an SLB-IL100 ionic liquid column

Gas chromatography (GC) of docosenoic acid (22:1) has been performed for the separation of positional isomers on the novel SLB-IL100 column with a highly polar ionic liquid stationary phase. A test mixture of 22:1 methyl esters prepared from total lipids of flounder was subjected to GC on a 60 m×0.32 mm i.d. column at an isothermal temperature of 150°C-180°C. On this column, all five positional isomers separated in the elution order of 22:1n-15, 22:1n-13, 22:1n-11, 22:1n-9, and 22:1n-7. The positional isomers, 22:1n-15, 22:1n-13, and 22:1n-11, unresolvable on conventional polar polymer phase columns, were almost completely separated from each other within 24 min at 170°C. The equivalent chain length values of 22:1n-11 to 22:1n-7 were parallel to those on polyethylene glycol and cyanopropyl polysiloxane columns, whereas 22:1n-15 and 22:1n-13 were relatively lower and closer to saturated 22:0 acid. Similar findings were also obtained for co-injected 20:1n-15 to 20:1n-11 isomers. Analysis of fish 22:1 revealed that 22:1n-13 is not always a minor isomer, as previously reported for several samples. The results of this study confirm the view that SLB-IL100 is a powerful tool for GC analysis of monounsaturated fatty acids.