Solid phase extraction and enrichment of essential fatty acid methyl esters from soy-derived biodiesel by novel π-complexing sorbents

The essential fatty acid (EFA) methyl esters, methyl linolenate (18:3) and methyl linoleate (18:2), were extracted and enriched from soy-derived biodiesel using novel π-complexing sorbents. These π-complexing sorbents were prepared by covalently immobilizing ionic liquids (ILs) onto silica and then coating these silica-supported ILs with silver salts. The silica-supported hydrophobic ILs enhanced the retention of silver salts on the solid sorbents. After the extraction of the polyunsaturated fatty acid methyl esters (PUFAMEs) 18:3 and 18:2 from biodiesel using the sorbents, a decrease in NOx emissions and an enhancement of the oxidation stability of biodiesel can be obtained. Solid phase extraction was investigated using a simple three-step procedure consisting of (1) sorbent pre-treatment, (2) sample extraction onto the sorbent and (3) stripping the sorbent by desorption solvent. The factors influencing extraction capacity and selectivity were also studied. 10.5 Mg of sorbent AgBF4/SiO2·Im+·PF6- could completely adsorb the 18:3 (0.66 mg) from standard biodiesel hexane solution in 5 min. After a consecutive two-step stripping by diethyl ether and 1-hexene, the 18:3 concentration (wt.%) was increased from around 8.5% in the original biodiesel hexane solution to approximately 90% in the 1-hexene stripping solvent.