Validation and long-term assessment of an approach for the high throughput determination of lipophilicity (log POW)...

A critical evaluation of the use of 96-capillary multiplexed microemulsion electrokinetic chromatography (MMEEKC) for the indirect determination of octanol-water partition coefficients (log POW values) for a wide range of structurally different compounds is presented. The various components of the microemulsion solution were evaluated and optimized for use in a multiplexed capillary format. A six-component calibration mixture and 23 different solutes (n = 4 each) were analyzed simultaneously, providing a throughput of up to 46 samples/h, which translates to greater than a 20-fold improvement over existing indirect log POW methods. Agreement to within +/-0.5 log P units of literature values was obtained for 51 of the 54 tested neutral and basic (uncharged) solutes. A linear free energy relationship (LFER) analysis performed on the MMEEKC system supports its use as a viable and effective model of the classical shake-flask method for log POW determinations. Moreover, a standard deviation of 0.1 or less log P units was obtained for 35 of 36 solutes analyzed repeatedly over an 8-month time period, documenting the long-term effectiveness of the analysis format. Critical comparisons between the proposed MMEEKC method and existing separation methods for the indirect determination of log POW values are also made. Overall, the results indicate that 96-capillary MMEEKC can serve as a high throughput, cost effective and robust approach and as a valid model for log POW determinations.