The development of a weak anion micro-capillary film for protein chromatography

•A weak micro-capillary film anion exchanger was developed.•Full characterisation of the membrane and the ion exchanger was conducted.•The exchanger was shown to separate anionic molecules to high purity.•Our results suggest that this device could be used for residual DNA clearance.

In this study, the surface of a microporous walled micro-capillary film (MMCF) was modified into a weak anion exchanger by coupling cyanuric chloride and 2-diethylaminoethylamine (DEAE) to the ethylene-vinyl alcohol (EVOH) matrix. Fourier transform infrared spectroscopy (FTIR) measurements of modified and unmodified MMCFs confirmed the addition of a triazine ring and DEAE onto the membrane. Binding of bovine serum albumin (BSA) at pH 7.2 was found to follow a Langmuir isotherm with a maximum equilibrium binding of 12.4 mg BSA/mL adsorbent and 8.2 mg BSA/mL adsorbent under static and flow conditions, respectively. The ion exchange capacity, determined by Mohr's titration of chlorine atoms displaced from the functionalised surface, was found to be 195 ± 21 μmol Cl−/mL of adsorber, comparable to commercial ion exchangers. BSA adsorption onto the ion exchanger was strongly pH-dependant, with an observed reduction in binding above pH 8.2.Frontal experiments of a BSA (5 mg/mL) and lysozyme (5 mg/mL) mixture demonstrated successful separation of BSA from lysozyme at more than 97% purity as verified by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Separation between similarly charged anionic molecules was also achieved using BSA (5 mg/mL) and herring sperm DNA (0.25 mg/mL). BSA was extracted at 100% purity, demonstrating the ability of MMCF-DEAE to remove significant DNA contamination from a protein solution. These experiments highlight the potential for MMCFs to be used for fast protein purification in preparative chromatography application.