Lipophilicity by Partition Chromatography

The partition of the compound between stationary phase (in most cases octadecane bonded on silica) and mobile phase is used as surrogate parameter for lipophilicity. The retention time of the analyte correlates with the lipophilicity of the compound. 

20 il of a 10 mM compound solution in DMSO are injected in the HPLC. The 1 cm column is used for high log D with a flow rate of 10 ml/minutes, whereas the compounds with low lipophilicity (logD 1.5) are characterized with the 25 cm column at a flow rate of 2 ml/min. In order to avoid octanol loss on the column due to the DMSO, the direction of injections is reversed with every sample. 

The capacity value (retention time - column dead time) is used for the calculation of the log D. For this purpose a standard set of compounds with known log D7.4 is used for calibration of the system. 

CRITICAL ASSESSMENT OF THE METHOD The method gives high quality data with very good correlation with traditional shake flask (Slater) derived log Ds. The method is not suited for compounds with very low lipophilicity log D -1, because for those no retention on the stationary phase is achieved. The other limitation are compounds with a lipophilicity 4.5. 

Due to the long retention time the peaks become no longer detectable. Furthermore, the method is limited to compounds with chromophors. The throughput of the method is about 20-40 compounds a day. 

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