Characterisation of grafted weak anion-exchange methacrylate monoliths.

A weak ion-exchange grafted methacrylate monolith was prepared by grafting a methacrylate monolith with glycidyl methacrylate and subsequently modifying the epoxy groups with diethylamine. The thickness of the grafted layer was determined by measuring permeability and found to be approximately 90nm. The effects of different buffer solutions on the pressure drop were examined and indicated the influence of pH on the permeability of the grafted monolith. Protein separation and binding capacity (BC) were found to be flow-unaffected up to a linear velocity of 280cm/h. A comparison of the BC for the non-grafted and grafted monolith was performed using beta-lactoglobulin, bovine serum albumin (BSA), thyroglobulin, and plasmid DNA (pDNA). It was found that the grafted monolith exhibited 2- to 3.5-fold higher capacities (as compared to non-grafted monoliths) in all cases reaching values of 105, 80, 71, and 17mg/ml, respectively. It was determined that the maximum pDNA capacity was reached using 0.1M NaCl in the loading buffer. Recovery was comparable and no degradation of the supercoiled pDNA form was detected. Protein z-factors were equal for the non-grafted and grafted monolith indicating that the same number of binding sites are available although elution from the grafted monolith occurred at higher ionic strengths. The grafted monolith exhibited lower efficiency than the non-grafted ones. However, the baseline separation of pDNA from RNA and other impurities was achieved from a real sample.