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J Sep Sci. 2013 Dec;36(24):3830-6.

Octanol/water partitioning simulation by RP-HPLC for structurally diverse acidic drugs: comparison of three columns in the presence and absence of n-octanol as the mobile phase additive.


The advantageous effect of n-octanol as a mobile phase additive for lipophilicity assessment of structurally diverse acidic drugs both in the neutral and ionized form was explored. Two RP C18 columns, ABZ+ and Aquasil, were used for the determination of logkw indices, and the results were compared with those previously reported on a base-deactivated silica column. At pH 2.5, the use of n-octanol-saturated buffer as the mobile phase aqueous component led to high-quality 1:1 correlation between logkw and logP for the ABZ+ column, while inferior statistics were obtained for Aquasil. At physiological pH, the correlations were significantly improved if strongly ionized acidic drugs were treated separately from weakly ionized ones. In the latter case, 1:1 correlations between logD7.4 and logkw(oct) indices were obtained in the presence of 0.25% n-octanol. Concerning strongly ionized compounds, adequate correlations were established under the same conditions; however, slopes were significantly lower than unity, while large negative intercepts were obtained. According to the absolute difference (diff = logD7.4 – logkw) pattern, base-deactivated silica showed a better performance than ABZ+, however, the latter seems more efficient for the lipophilicity assessment of highly lipophilic acidic compounds. Aquasil may be the column of choice if logD7.4<3 with the limitation, however, that very hydrophilic compounds cannot be measured.

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