SYNTHESIS AND USE OF QUATERNIZED POLYETHYLENIMINE-COATED ZIRCONIA FORHIGH-PERFORMANCE ANION-EXCHANGE CHROMATOGRAPHY

The synthesis of an alkali-stable strong anion-exchange stationary pha se by deposition of polyethylenimine (PEI), followed by cross-linking and quaternization, onto porous zirconia particles is described. Physi cal characterization of quaternized PEI-zirconia and PEI-zirconia show s that 50% and 24% of the amine groups are cross-linked, respectively. A plot of log k' versus log (competing ion concentration) is linear f or three homopeptides, suggesting that ion exchange is the primary mec hanism of retention on quaternized PEI-zirconia. Column efficiency for two 2,4-dinitrophenyl amino acids increased by 80% upon increasing th e temperature from 50 degrees C to 100 degrees C. The hydrophobicity o f quaternized PEI-zirconia was studied using a homologous series of p- alkoxybenzoic acids, For quaternized PEI-zirconia and PEI-zirconia, we found that the free energy of transfer of a methylene unit from the m obile phase to the stationary phase was -2.0 and -0.90 kJ/mol, respect ively. The free energy of transfer of a methylene unit on quaternized PEI-zirconia is similar to that of a typical ODS phase (-2.4 kJ/mol). A van't Hoff plot for the above two 2,4-dinitrophenyl amino acids show ed that the enthalpies of transfer are exothermic and fairly large (si milar to -14 kJ/mol). Isocratic separations on quaternized PEI-zirconi a of inorganic and organic anions are presented. Quaternized PEI-zirco nia, quaternary amine-functionalized silica, and PEI-zirconia are comp ared chromatographically. Quaternized PEI-zirconia is more efficient t han the silica-based phase in the separation of benzoic acid derivativ es but slightly less efficient than PEI-zirconia. The major virtue of quaternized PEI-zirconia is that it is chemically stable in the pH ran ge of 1-13 and is also stable at temperatures up to 100 degrees C.