ANYL 129 |
| Docosylsilane (C22) stationary phases1 offer increased selectivity for rigid solutes compared to octadecylsilane (C18) stationary phases and are commonly used for the separation of polycyclic aromatic hydrocarbons. In understanding the molecular basis of this effect, Raman spectroscopy is used to investigate the effects of mobile phase solvents on alkyl chain rotational and conformational order in a series of high-density C22 stationary phases using empirical spectral indicators. Experimental results indicate that alkyl chain rotational and conformational order is dependent on solvent characteristics and stationary phase properties. In general, polar solvents slightly increase order of the alkyl chains, whereas nonpolar solvents slightly disorder the alkyl chains. Raman spectroscopy is sensitive to subtle changes in the solvated conformation of the stationary phases as a function of surface coverage, nature of the alkylsilane precursor and preparation method (surface or solution polymerized). From these results, molecular pictures of these solvent-stationary-phase interfaces are proposed. 1The authors gratefully acknowledge Dr. Lane C. Sander of the National Institute of Standards and Technology for the kind gift of the high-density C22 stationary phases. |
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General Papers
7:00 PM-9:00 PM, Sunday, 28 August 2005 Washington DC Convention Center -- Hall A, Poster
Sci-Mix
Division of Analytical Chemistry |