A Comparison Of Two Stationary Phases Of Lipophlicity Measurement By RP-HPLC

Object: A set of 11 model solutes and drugs were selected to determine their extrapolated logkw of the retention factor logk by Reversed-Phase High-Performance Liquid Chromatography (RP-HPLC)in two different stationary phases. Compared the correlations of capacity factors logkw and the lipophilicity partition coefficients (logP_oct) in two stationary phases. The mechanisms of retention on both stationary phases and the mechanisms of the solutes'partition in octanol/water system were assessed and compared to study the feasibility of rapidly determining lipophilicity by RP-HPLC. Method: XTerra RP 18 stationary phase and YMC-Pack ODS-A stationary phase were applied as the stationary phases to determine 11 solutes'logk and extrapolated to 100% H2O (buffer)logkw and established the Linear regression equation of logkw and logP_oct. Used JMP 6.0 to study the mechanisms of retentions of these solutes in both stationary phases by Linear salvation/free-energy relation(LSER).Results XTerra RP 18 Linear regression equation of logkw and logP_oct logP_oct=0.79(±0.07)logkw+0.71(±0.15) n=11, r²=0.94, F= 139 YMC-Pack ODS-A Linear regression equation of logkw and logP_oct logP_oct=0.73(±0.10)logkw+0.44(±0.29) n=11, r²=0.85, F=50 XTerra RP 18 Linear regression equation of logkw and structure parameters logkw(XTerra RP 18)=3.49·10^-2(±0.38·10^-2)Vm -0.41(±0.15)Ï€* -3.61(±0.49)β-0.65(±0.19) n=11, r²=0.97, F=78 YMC-Pack ODS-A Linear regression equation of logkw and structure parameters logkw(YMC-Pack ODS-A)=3.95·10^-2(±0.38·10^-2)Vm -0.85(±0.15)Ï€* -3.54(±0.49)β+0.37(±0.24)α-0.34(±0.20) n=11, r²=0.98, F=68 Linear regression equation of logP_oct and structure parameters logP_oct=2.91·10^-2 (±0.41·10^-2) Vm -0.29(±0.16)Ï€*-3.28(±0.54)β-0.19(±0.21) n=11, r²=0.95, F=43Conclusion: the capacity factors logkw obtained with the XTerra RP 18 phase was more closely related to experimental logP_oct values than the logkw obtained with the YMC-Pack ODS-A phase. LSER analyses showed that the retention mechanisms of the two stationary phases are different. Retention mechanisms of the XTerra RP 18 phase and the mechanisms of the solutes'partition in octanol/water system are similar. Accordingly, the polar embedded ligands phase XTerra RP 18 phase is more suitable for the rapidly determining lipophilicity.