Selective binding of docosahexaenoic acid ethyl ester to a silver‐ion‐loaded porous hollow‐fiber membrane

Silver ions were loaded at a density of 1 mmol/g onto a sulfonic acid group‐containing porous hollow‐fiber membrane prepared by radiation‐induced graft polymerization of an epoxy group‐containing monomer with subsequent modification by reaction with sodium sulfite. The permeability (i.e., permeation flow rate per inside surface area of the hollow fiber) of 4.6% wt/vol bonito oil ethyl ester solution in water/ethanol (7.5:92.5, vol/vol) was 1.7 m/h at a permeation pressure of 0.1 MPa. Breakthrough curves (i.e., concentration changes of the effluent with increasing effluent volume) obtained with docosahexaenoic acid ethyl ester (DHA‐Et) overlapped, irrespective of the permeation flow rate. This indicates that a higher rate of DHA‐Et adsorption onto the silver ions on the membrane was attained with increasing permeation flow rate. DHA‐Et, which was selectively bound to the membrane, was quantitatively eluted with acetonitrile as an eluent. The adsorption characteristics (i.e., binding rate, selectivity and durability for repeated use) of DHA‐Et using the silver ion loaded porous hollow‐fiber membrane were demonstrated. Feasibility studies will enable comparison of the purification cost of DHA‐Et among the other purification techniques.