Hexamethyldisiloxane as a mobile phase component for normal phase liquid chromatography

Abstract

Hexamethyldisiloxane (HMDX) has been evaluated as a modifier solvent for the normal phase separation of substituted naphthalene componds as well as aromatics such as nitrobenzene, acetophenone, benzonitrile, and aniline. It is found to be a weaker eluting solvent than n-butyl ether and other commonly used normal phase solvents filling a niche in the eluotropic series. HMDX exhibited an unusual retention factor (k′) profile as a function of mobile phase composition in hexane. In a range from 0 to 40 %, thek′ values remained quite constant with increasing HMDX composition. As the concentration of HMDX progressed to 100 %, thek′ values actually increased in a generally linear fashion. This trend ink′ is due to longer solute retention not just a change in the retention time of the unretained component. Although slight silanization of the silica column may occur with initial use of HMDX, retention of these analytes on a commerical C-1 silica column is much lower with no positivek′ slope with increasing HMDX. The chromatographic data provide evidence that HMDX is likely adsorbed to the silica surface and a solute partitioning mechanism may be operative.