Correlations between octanol-water partition coefficients and reversed-phase high-performance liquid chromatography capacity factors : Chlorobiphenyls and alkylbenzenes

Abstract

The capacity factors ( k′ ϕ) of 4 chlorobiphenyls and 39 alkylbenzenes (C 1—C 10) were determined using reversed-phase high-performance liquid chromatography at eight different mobile phase compositions (ϕ = 50–90% acetonitrile in water). The predicted capacity factors in water (log k′ 0) were determined by linear regression of log k′ ϕ and the acetonitrile concentration. Comparison of log k′ 0 data from two solvent systems (acetonitrile—water, methanol—water) with published data indicates that this parameter is dependent on both the mobile phase and the chromatographic system used in determining log k′ ϕ. The determined log k′ 0 values and n-octanol—water partition coefficients (log P oct) taken from the literature were analyzed by linear regression. Log P oct estimates made from separate regressions using the individual and combined compound classes are presented and compared. The slopes of the lines for the two compound classes were similar, but each had distinctly different intercepts. Log P oct estimates resulting from the individual compound class regressions agreed more closely with published data than did estimates derived by combining the two classes during regression. It is recommended that separate regressions be developed for each compound class of interest. Log P oct estimates for the alkylbenzenes were also made using fragment constants. The fragment constants were compared with structural group factors derived from the log k′ 0 based estimates. It is noted that the substitution pattern of the benzene ring affects these group factors.