ESTIMATION OF HYDROPHOBICITY USING QUASI-MOLECULAR VOLUME OF QUATERNARY AMMONIUM IONS

Abstract

When the Cu(II), Co(III), Ni(II), and Fe(II) chelates with 2-(5-Nitro - 2-pyridyl - 5 - [N-propyl-N-sulphopropyl)amino]phenol (Nitro-PAPS) were separated on octadecylsilane (ODS) stationary phase (Kaseisorb ODS Super and Kaseisorb LC ODS-300-5) by the addition of several quaternary ammonium salts (Q⁺Br-) individually to the aqueous ACN mobile phase, a correlation of these hydrophobic cation's character with the retention of the chelates was examined. The degree of the variation of the stationary phase due to the adsorption of quaternary ammonium ion (Q⁺) is measured by using a series of elution time of a solute, which was obtained by its successive injection. When the alkyl group of Q⁺ is larger, the period for attaining the equilibrium becomes longer. As a concentration of Q⁺ is higher, the period becomes longer.

The estimation of quasi-molecular volume is proposed. The estimation volume provides its first order relationship with log k′ of the metal chelates, regardless of the difference of its charged position in the structure. The degree of the slope of the first order relationship corresponds to the number of Q⁺ associated with metal/Nitro-PAPS chelate. The elution order corresponds to the total number of Q⁺ and Nitro-PAPS being associated with metal ions.

Acknowledgments