Improved endcapping method of monolithic silica columns

Following a bonding reaction with octadecyldimethyl-N,N-diethylaminosilane (ODS-DEA), a monolithic silica was subjected to consequential on-line endcapping reactions with hexamethyldisilazane (HMDS) or N-(trimethylsilyl)imidazole (TMSI) to compare the two reagents. Endcapping of monolithic silica C-18 columns prepared by a manufacturer was also studied. After endcapping with TMSI in acetonitrile (ACN), all columns provided better performance for hydrogen-bonding compounds and basic compounds than C-18 phases endcapped with HMDS. TMSI endcapping of commercial Chromolith Performance columns also gave improved performance. The results indicate that one can significantly improve the performance of monolithic silica C-18 columns for basic compounds by a simple on-column reaction with TMSI in ACN at a relative low temperature. (c) 2006 Elsevier B.V. All rights reserved.