6533b855fe1ef96bd12b1b03

RESEARCH PRODUCT

Structure and properties ofn-alkyldimethylsilyl bonded silica reversed-phase packings

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Summary The effects of the modifier functionality and the chain length ofn-alkylchlorosilanes on the surface structure of packings and on their retention behaviour in reversed-phase chromatography were investigated. Comparative retention studies on three silica packings that had been treated to maximum conversion withn-octyltrichlorosilane (I),n-octylmethyldichlorosilane (II) andn-octyldimethylmonochlorosilane (III) showed that the most pronounced reversed-phase character is obtained by using III as the modifying reagent. A series ofn-alkyldimethylsilyl bonded silica packings were prepared with widely differingn-alkyl chain lengths. Although the packings are very hydrophobic, the maximum surface concentration is 2–4 μmole/m2 and a high population of hydroxyl groups (ca. 3–4 μmole/m2) can still be detected by the isotopic exchange method. The retention characteristics of hydrocarbons in methanol-water as the eluent were measured on these packings. The variation of the capacity factors of solutes could be well correlated with the following molecular quantities that characterize the solute and the type of bonded group: the total hydrocarbonaceous surface area of the bondedn-alkyldimethylsilyl group, the total hydrocarbonaceous surface area of the solute and the molecular dipole moment of the solute.