Investigation of order and disorder in liquid chromatographic stationary phases by molecular dynamics simulations

ANYL 236

Katrice A. Lippa, katrice.lippa@nist.gov1, Lane C. Sander, lane.sander@nist.gov1, and Raymond D. Mountain, rmountain@nist.gov2. (1) Analytical Chemistry Division, National Institute of Standards and Technology, MS 8392, 100 Bureau Drive, Gaithersburg, MD 20899-8392, (2) Physical and Chemical Properties Division, National Institute of Standards and Technology, 100 Bureau Drive Stop 8380, Gaithersburd, MD 20899-8380
In an effort to elucidate the molecular-level structural features that control shape-selective separations, we have investigated the molecular dynamics of chromatographic models that represent both monomeric and polymeric reversed-phase liquid chromatography (RPLC) stationary phases with alkylsilane density and length and temperature conditions analogous to actual materials of low to high shape selectivity. The structural characterization of these models is consistent with previous experimental observations of order and disorder: alkyl chain order increases with chain length, surface coverage and with reduced temperature. The alkyl chain closest to the silica substrate surface is disordered (primarily gauche dihedral angle conformations) and the opposite end is most ordered (trans conformations). Models that represent highly shape selectivity RPLC phases contain well-defined alkyl chain cavities comprised of primarily trans conformations; the size and depth of these “slots” increase for the C30 models, which may promote the enhanced separations of larger size shape-constrained solutes, such as carotenoids.

 

General Papers
7:00 PM-9:00 PM, Sunday, 28 August 2005 Washington DC Convention Center -- Hall A, Poster

Sci-Mix
8:00 PM-10:00 PM, Monday, 29 August 2005 Washington DC Convention Center -- Hall A, Sci-Mix

Division of Analytical Chemistry

The 230th ACS National Meeting, in Washington, DC, Aug 28-Sept 1, 2005