TY - JOUR
T1 - Structure-function relationships in high-density docosylsilane bonded stationary phases by Raman spectroscopy and comparison to octadecylsilane bonded stationary phases
T2 - Effects of common solvents
AU - Liao, Zhaohui
AU - Pemberton, Jeanne E.
PY - 2008/4/15
Y1 - 2008/4/15
N2 - The effects of common solvents on alkyl chain conformational order in a series of high-density C22 stationary phases with surface coverage ranging from 3.61 to 6.97 μmol/m2 are investigated by Raman spectroscopy. Conformational order is evaluated using the intensity ratio of the antisymmetric and symmetric v(CH2) modes as well as the frequencies at which these Raman bands are observed. Solvents studied include methanol-d4, acetonitrile-d3, water-d2, toluene-d8, chloroform-d. and benzene-d6. Alkyl chain conformational order and, hence, solvation of the stationary phase, is dependent on the Gibbs free energy change for these molecules at infinite dilution in hexadecane (ΔG HD○), as well as stationary-phase properties (polymerization method and surface coverage). In general, polar solvents increase slightly the conformational order of these C22 stationary phases, while non-polar solvents decrease conformational order. A comparison is made between C22 and C18 bonded-phase systems to further understand the role of alkyl chain length on solvent-stationary phase interactions. The change in alkyl chain conformational order induced by solvent is also compared to that induced by temperature, which provides insight into the effect of chromatographic conditions on stationary-phase shape selectivity, an important application of these materials.
AB - The effects of common solvents on alkyl chain conformational order in a series of high-density C22 stationary phases with surface coverage ranging from 3.61 to 6.97 μmol/m2 are investigated by Raman spectroscopy. Conformational order is evaluated using the intensity ratio of the antisymmetric and symmetric v(CH2) modes as well as the frequencies at which these Raman bands are observed. Solvents studied include methanol-d4, acetonitrile-d3, water-d2, toluene-d8, chloroform-d. and benzene-d6. Alkyl chain conformational order and, hence, solvation of the stationary phase, is dependent on the Gibbs free energy change for these molecules at infinite dilution in hexadecane (ΔG HD○), as well as stationary-phase properties (polymerization method and surface coverage). In general, polar solvents increase slightly the conformational order of these C22 stationary phases, while non-polar solvents decrease conformational order. A comparison is made between C22 and C18 bonded-phase systems to further understand the role of alkyl chain length on solvent-stationary phase interactions. The change in alkyl chain conformational order induced by solvent is also compared to that induced by temperature, which provides insight into the effect of chromatographic conditions on stationary-phase shape selectivity, an important application of these materials.
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U2 - 10.1021/ac702270b
DO - 10.1021/ac702270b
M3 - Article
C2 - 18336011
AN - SCOPUS:42349084089
SN - 0003-2700
VL - 80
SP - 2911
EP - 2920
JO - Analytical Chemistry
JF - Analytical Chemistry
IS - 8
ER -