A novel sulfonic acid false(SO3Hfalse) group containing membrane (SH membrane) was prepared by grafting glycidyl methacrylate onto an ethylene‐tetrafluoroethylene copolymer film with subsequent sulfonation. The graft chains introduced on the SH membrane form a flexible brush‐type structure capable of binding water molecules (30% more than Nafion 117 membrane) and transporting protons. Proton conductivity of the SH membrane was evaluated as a function of SO3H group density. The SH membrane with the SO3H group conversion of 97% and the thickness of 70 μm had a specific resistivity of 24 Ω cm at 303 K, which was comparable to that of Nafion 117 membrane. A uniform distribution of the SO3H group across the SH membrane was verified using an electron probe x‐ray microanalyzer.

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.Paper no. J8978 in JAOCS 76, 771-775 (July 1999).KEY WORDS: Bonito oil, DHA, permeation flow, porous hollow-fiber membrane, silver ion binding.Eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) are representative long-chain n-3 fatty acids. Since EPA and DHA are powerful competitive inhibitors of lipoxygenases and cyclooxygenases, the intake of these polyunsaturated fatty acids (PUFA) may have fundamental consequences for cellular and tissue functions. DHA is considered to be a promising pharmaceutical because of its beneficial effects on the retina and brain (1).Conventionally, DHA has been purified by vacuum distillation, column chromatography using octadecyl-group-containing silica beads, and supercritical fluid extraction. Stein and Slawson (2) used silicic acid-silver nitrate adsorbents for chromatography, based on a weak interaction between silver ions and the double bonds of PUFA. Recently, liquid extraction using a silver nitrate aqueous solution has been proposed (3). A liquid membrane using the silver nitrate aqueous solution as the water phase was applied for the extraction of EPA (4) and PUFA (5). Moreover, a silver ion-loaded cation-exchange membrane exhibited considerable differences in the permeability rates of PUFA with different numbers of double bonds (6). A silver ion-sandwiched clay material has been suggested for DHA purification (7). We have prepared porous membranes containing functional groups: chelating porous membranes (8) for collecting metal ions, and ion-exchange (9), hydrophobic (10) and affinity (11,12) porous membranes for collecting proteins. These membranes realize a high collection rate because of convectionaided transport of target ions and proteins to the functional groups. Membrane chromatography using porous functional me...