Calculated Log Kow as a Guide for Key-Set Mobile Phase Selection in Retention Prediction
Charles H. Lochmuller, M. Hui · Journal of Chromatographic Science · 1998
Previous reports have demonstrated that the relative solvent strength relationship is transferable between similar columns (e.g., C18 packing). Method transfer between columns is realized using a “key-set” solvent projection matrix derived from measurements on one column and measurements for compounds in a key combination mobile phase set on each new column. This paper offers a solution to the problem facing the method developer in selecting the best mobile phases as a “key set” to predict the behavior of solutes in other mobile phases of similar composition. Given the known relation of log Kow (or log P) and In k′ to the free-energy change on transfer, one can estimate the k′ value range for new compounds in each previously studied mobile phase. The key-set mobile phases are selected using calculated log Kow as the three to five best-ranked solvents with k’ predicted to be between 0.5 and 10. Retention data are collected for 19 new compounds in 20 water—methanol—acetonitrile mobile phases on two different C18 columns. The average cross-column prediction error based on k′ for a three-factor model is 6%.