Application of different RP-HPLC methods for the determination of the octanol/water partition coefficient of selected tetrachlorobenzyltoluenes

Reversed-phase high-performance liquid chromatography (RP-HPLC) in both, is ocratic and gradient elution mode (stationary phase: LiChrospher 100 RP-18; mobile phase: water/methanol or water/acetonitrile) was used for a renewed determination of octanol/water partition coefficients (K-OW) of selected t etrachlorobenzyltoluene (TCBT) isomers. Reported K-OW values identify this substance class as very hydrophobic but the data are relatively inconsisten t. Based on a series of calibration runs with hydrophobic reference substan ces of different chemical structure at various eluent compositions we teste d different approaches for the evaluation of isocratic retention factors (l ogk) and found substantial differences between the direct calibration proce dure at special methanol volume fractions in the mobile phase (0.95-0.80) a nd the use of retention factors extrapolated to pure water as eluent (log k (W)). The log K-OW values obtained for the TCBTs with the latter approach a re around 0.5 units higher and closer to literature data. The gradient elut ion experiments yield slightly better results compared to the isocratic dir ect calibration procedure, but not as good as the calibration with logk(W). In addition, the use of the RP-HPLC retention factors for estimating sorpt ion coefficients (K-OC) of TCBT isomers is discussed. (C) 2001 Elsevier Sci ence Ltd. All fights reserved.