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Two polar bonded phases, phenyl-silica and cyanopropylsllica, have been studied under reversed-phase conditions using homologues of alkanoate and perfluoroalkanoate esters as test solutes. For comparative purposes a similarly prepared n -butyl phase also has been studied under equivalent conditions. Retention measurements have been carried out as a function of mobile-phase composition for water-methanol and water-acetonitrile and Incremental methylene (-CH2-) and perfluoromethylene (~CF2~) selectlvltles calculated. These latter data have been used to estimate the thermodynamic constant K^, which describes the sorption equilibrium of solvents between mobile and stationary phases assuming Ideality of these phases. For water-methanol, differences In composition between the mobile and surface phases due to preferential Intercalation are small. However, the data Indicate a significant sorption excess of acetonitrile by the bonded phases. This preferential sorption of acetonitrile Is greatest for alkyl phases and decreases with increasing polarity of the bonded phase (l.e., cyano-silica < phenyl-silica < alkyl-silica).

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