Microwave-assisted, grafting polymerization preparation of strong cation exchange nylon 6 capillary-channeled polymer fibers and their chromatographic properties

• A microwave-assisted method of grafting sulfonic acid ligands is described for the first time for chromatographic phases.
• A high-density, strong cation exchange surface is created on a nylon 6 C-CP fiber support.
• Vast improvements in dynamic loading capacity and chromatographic performance are realized over native nylon 6 phases.
• Modification of the fiber surface introduces no deleterious effects on the column kinetic performance.

Native nylon 6 C-CP fibers were modified with 2-acrylamido-2-methylpropanesulfonic acid (AMPS) via the microwave-assisted grafting polymerization to affect a strong cation exchange stationary phase. Various concentrations of AMPS and the initiator potassium persulfate (KPS) were used in the modifications. The resultant nylon-SO3H fibers were characterized by Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM) and acid-base titrations. The chromatographic properties, including column permeability, protein separation quality, and protein binding capacity, of the nylon-SO3H fiber columns were also studied. The cation exchange ligand densities on the modified fibers (SO3H) were determined to be 50–317 μmol g−1, in comparison to the cation (COOH) density of 28 μmol g−1 of native nylon 6 fibers. The modified fiber phase showed increased lysozyme dynamic loading capacities (up to ∼13 mg mL−1 bed volume) at a linear velocity of ∼90 cm min−1, while native nylon 6 showed only ∼1 mg mL−1 lysozyme loading capacity. Fast (30 s–3 min) gradient separations of myoglobin, α-chymotrypsinogen A, and lysozyme were achieved on nylon-SO3H columns, with the separation resolution and peak capacity characterized. The efficiency of surface re-equilibration was probed with an eye toward using the phase as the second dimension in comprehensive two-dimensional liquid chromatography (2D-LC). The results indicate that this nylon-SO3H fiber phase has a good deal of potential for use in high-throughput analytical and preparative protein separations.

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