Evaluation of the Gibbs free energies of tris(β-diketonato) chromium (III),-cobalt(III), and bis(β-diketonato)palladium(II) in reversed-phase liquid chromatography on octadecyl-bonded silica gel with acetonitrile-water mobile phases

Abstract

Key WordsColumn liquid chromatography Gibbs free energy Octadecyl-bonded silica gel Liquid-liquid partition coefficient SummaryTo clarify the mechanism of retention of several fldiketonates of chromium(III), cobalt(III), and palladium(II) in reversed-phase liquid chromatography (RPLC), their capacity factors (k) were measured on an octadecyl-bonded silica gel (ODS) stationary phase with acetonitrile-water binary mobile phases. The values obtained were compared with the liquid-liquid partition coefficients (P) of the metal fl-diketonates in the dodecane/(acetonitrile-water mixture) system. This comparison showed that with regard to the distribution of the metal fl-diketonates the nature of the stationary phase was similar to, but not identical with, that of dodecane. When the Gibbs free energies of the metal fldiketonates in the stationary phase were calculated, the values showed that the cavity-formation free energy for each metal fl-diketonate in the stationary phase was close to that in dodecane, and the interaction free energy was almost equal to the sum of the energies of interaction with the alkyl moiety and with acetonitrile. This implies that acetonitrile molecules from the mobile phase penetrate the alkyl moiety of ODS.

Analytical Aspects of Metal Enolates

“…The van't Hoff plots showed that platinoid metal β-diketonates operate on the same retention mechanism at 25-45 • C. Optimum conditions for the separation of four platinoid metal β-diketonates are: 40% MeOH, polymeric C 18 column and 45 • C 165 . In order to clarify the mechanism of retention of several β-diketonates of chromium(III), cobalt(III) and palladium(II), their Gibbs free energies were evaluated in RP-LC on C 18 more quantitative treatment of the Gibbs free energy of the interaction of solutes with the stationary phase, which is in accordance with the additivity of Gibbs free energy 166 . Capacity factors have been measured for several β-diketonates of Cr(III) and Pd(II) on C 18 -bonded silica stationary phases with a MeOH-H 2 O mobile phase.…”