Preparation of Chiral Ligand Exchange Chromatographic Stationary Phase by Atom Transfer Radical Polymerization for Separation of Racemates

A novel stationary phase was synthesized for chiral ligand exchange chromatography(CLEC) via atom transfer radical polymerization(ATRP) method. Poly (1-acryloylpyrrolidine-2-carboxylic acid) polymer brush was grafted onto the surface of the silica by ATRP using 2-bromoisobutyryl bromide as an initiator, and the organic metal compound formed in the CuCl/2,2'-bipyridine(Bpy) system as a catalyst in water medium at room temperature. Three high-capacity chiral stationary phases obtained with different ATRP formulations were tried as chromatographic packings in CLEC. The stationary phases were characterized by means of elementary analysis and thermogravimetric analysis. The influence of the ligand grafted-density, mobile phase pH, concentration of Cu2+, temperature of column on the resolution of DL-amino acids by CLEC were investigated, and the optimized chromatographic conditions were selected. The thermodynamics for separatins of racemates was discussed. The results showed that the prepared columns could separate nine DL-amino acids and a-hydroxy acid with high separation factor, and high retentions. The DL-threonine, DL-tyrosine and DL-tryptophan could be simultaneously separated using the stationary phase. It could be proved that the entropy controlled the process of chiral separation.