Selective extraction and enrichment of polyunsaturated fatty acid methyl esters from fish oil by novel π-complexing sorbents

Novel π-complexing sorbents were prepared by covalently immobilizing ionic liquids (ILs) onto silica and then coating this silica-supported ILs with silver salts. These supported ILs exhibited a stronger ability to immobilize and retain silver salts on silica versus traditional π-complexing sorbents formed by direct anchoring of silver salts onto silica. These sorbents were successfully applied to extract and enrich polyunsaturated fatty acid methyl esters (PUFAMEs) from fish oil with both high selectivity and high capacity. The enrichment of PUFAMEs was investigated using a simple three-step procedure consisting of (1) sorbent pretreatment, (2) sample extraction onto the sorbent and (3) stripping the sorbent by 1-hexene or by diethyl ether first then 1-hexene. The preparation and characterization of the silica-supported ionic liquid phase were reported here. The factors influencing extraction capacity and selectivity were also studied. These included screening of various sorbents and stripping solvents, extraction time, sorbent quantity, and the pretreatment solvent. Only 5 mg of the sorbent AgBF4/SiO2·Im+·PF6− completely adsorbed 0.33 mg of the PUFAME, methyl ester of eicosapentaenoic acid (20:5) in 5 min from the feed mixture solution. The saturated extraction capacity for this 20:5 PUFAME by using this AgBF4/SiO2·Im+·PF6− was 120.0 mg/g as determined by its adsorption isotherm. After a consecutive two-step stripping by diethyl ether and then 1-hexene, the concentration of 20:5 increased from 7% in the feed stock solution to about 90% in the 1-hexene stripping solvent. After a total of six cycles, this sorbent still exhibited satisfactory reusability. The ability of this π-complexing sorbent to extract and enrich PUFAMEs from a cod liver oil matrix was also established.