Organically modified silica sol-mediated capillary electrophoresis.

We describe in this paper the use of ormosil (organically modified silica) sols as additives to the run buffer for selectivity manipulations between solutes in capillary electrophoresis. CE systems that contain sol additives in the run buffer can be thought of as pseudocapillary electrochromatography. Three sols based on different types of silanes were studied. Methyltrimethoxysilane (MTMOS)-based sol was found to improve selectivities between various aromatic acids. Aminopropyltrimethoxysilane (APS) sol interacts differently with structural isomers of aromatic acids than does MTMOS. At low pH with APS sol in the run buffer, neutral solutes can be separated, as well. The separation of the neutral solutes seems to be facilitated by the formation of hydrogen bonds between the solutes and the APS sol. APS and N-[3-(trimethoxysilyl)propyl]-ethylenediamine (EDAS) affect the separation of the same compounds differently, thus indicating that even small changes of the functional groups of the sol have pronounced effect on the interactions between the sols and the solutes.