Development of new urea-functionalized silica stationary phases - Characterization and chromatographic performance

New urea-functionalized silica stationary phases were prepared by a single- step surface modification through reaction of LiChrosorb Si100 (5 mum parti cle size) with a homologous series of alkoxysilanes, synthesized in our lab oratory, with the general formula (CH3CH2O)(3)Si(CH2)(3)NHC(O)NH(CH2)(n)CH3 , where n=4, 6 and 11. The modified silicas were characterized by elemental analysis of carbon and nitrogen, solid-state: Si-29- and C-13-cross polari zation magic angle spinning nuclear magnetic resonance and nitrogen adsorpt ion isotherms at 77 R. Chromatographic evaluation of the three urea-functio nalized silicas in 150x3.9 mm I.D. HPLC columns was carried out by the sepa ration of a test mixture composed of uracil, acetophenone, benzene, toluene and naphthalene, using acetonitrile-water as mobile phase. These new stati onary phases, with embedded polar urea groups, are very promising when comp ared with amide phases prepared by the conventional two-step modification p rocess. A single-step reaction process silica modification is better for ob taining a well-characterized and homogeneous modified surface. (C) 2001 Els evier Science B.V. All rights reserved.