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 C18 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 C18 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 C18 columns for basic compounds by a simple on-column reaction with TMSI in ACN at a relative low temperature.