EFFECT OF HAMMETT CONSTANT ON THE QUANTITATIVE CORRELATION OF BENZOIC-ACID RETENTION IN RP-IPC WITH N-OCTANOL WATER PARTITION-COEFFICIENTS

The quantitative correlation of n-octanol/water partition coefficient (logP) vs. extrapolated capacity factor (logk(ip)w) in RP-IPC and Hamm ett's constant (sigma) with eleven ionic benzoic aclas as model compou nds is evaluated. There is a high regression coefficient (0.98) with m ethanol and acetonitrile as organic modifiers, but there is a low regr ession coefficient (0.80) with tetrahydrofuran as organic modifier. Th e parameter logk(ip)w makes a positive contribution to n-octanol/water partition coefficient whereas the Hammett's constant makes a negative contribution. Methanol and acetonitrile are the solvents of choice fo r determination of logP value of the ionic solutes. The electronic eff ect of solutes described by the Hammett's constant plays a quite impor tant role in the retention of ionic compounds in RP-IPC.