Synthesis of an affinity adsorbent based on silica gel and its application in endotoxin removal

An affinity media for endotoxin removal based on silica gel was prepared by activation with silane coupling agent and subsequent conjugation with histidine (His) as a ligand. The influence of pore size and particle dimension of the silica gel and the grafting conditions such as reaction temperature and concentration of His in solution on the grafting yield of His were studied by means of IR, thermogravimetric analysis and elemental analysis. The results show that the silica gel with a particle size of 200 μm and a pore size of about 12 nm was a good carrier material for the preparation of the affinity adsorbent. Under the optimal conditions, histidine was covalently immobilized on silica gel at about 20 mg/g, with a corresponding maximum endotoxin adsorption capacity qm in contaminated water of about 1.2 mg/g and an apparent dissociation constant Kd of about 1350 μg/L. The adsorbent had little nonspecific adsorption from a protein-containing solution.