A novel evaluation method for extrapolated retention factor in determination of n-octanol/water partition coefficient of halogenated organic pollutants by reversed-phase high performance liquid chromatography

The retention factor corresponding to pure water in reversed-phase high performance liquid chromatography (RP-HPLC), k_w, was commonly obtained by extrapolation of retention factor (k) in a mixture of organic modifier and water as mobile phase in tedious experiments. In this paper, a relationship between log k_w and log k for directly determining k_w has been proposed for the first time. With a satisfactory validation, the approach was confirmed to enable easy and accurate evaluation of k_w for compounds in question with similar structure to model compounds. Eight PCB congeners with different degree of chlorination were selected as a training set for modeling the log k_w ? log k correlation on both silica-based C₈ and C₁₈ stationary phases to evaluate log k_w of sample compounds including seven PCB, six PBB and eight PBDE congeners. These eight model PCBs were subsequently combined with seven structure-similar benzene derivatives possessing reliable experimental K_ow values as a whole training set for log K_ow ? log k_w regressions on the two stationary phases. Consequently, the evaluated log k_w values of sample compounds were used to determine their log K_ow by the derived log K_ow ? log k_w models. The log K_ow values obtained by these evaluated log k_w were well comparable with those obtained by experimental-extrapolated log k_w, demonstrating that the proposed method for log k_w evaluation in this present study could be an effective means in lipophilicity study of environmental contaminants with numerous congeners. As a result, log K_ow data of many PCBs, PBBs and PBDEs could be offered. These contaminants are considered to widely exist in the environment, but there have been no reliable experimental K_ow data available yet.