Thermodynamic and Extrathermodynamic Studies of Enantioseparation of Imidazolinone Herbicides on Chiralcel OJ Column

Abstract

A homologous series of chiral imidazolinone herbicide was previously resolved on Chiralcel OJ column in high performance liquid chromatography. However, the mechanism of the chiral separation remains unclear. In this study, chromatographic behaviors of five chiral imidazolinone herbicides were characterized by thermodynamic and extrathermodynamic methods in order to enhance the understanding of the chiral separation. Thermodynamic parameters of this study were derived from equilibrium constant ( ) that was estimated from the moment analysis of the chromatographic peak. Van't Hoff plots of (ln versus 1/ ) were linear at a range of 15-50 ∘ C, only nonlinear at a range of 5-15 ∘ C with n-hexane (0.1%, trifluoroacetic acid)-2-propanol 60/40 (v/v) mobile phase. The enantiomer retention on the chiral column was entropy-driven at a lower temperature (5 ∘ C) and enthalpy-driven at a higher temperature (10 to 50 ∘ C). Enantioseparations of four of the five imidazolinone herbicides were enthalpy-driven, only entropy-driven for imazaquin. Enantioseparation mechanisms were different in between 5-10 ∘ C and 15-50 ∘ C probably due to the conformational change of the OJ phase. Enthalpy-entropy compensation showed similar mechanisms in retention and chiral separation for the five (−) or (+) enantiomers. Several extrathermodynamic relationships were able to be extracted to address additivity of group contribution.

Iniferter‐mediated grafting of molecularly imprinted polymers on porous silica beads for the enantiomeric resolution of drugs

“…As illustrated in Figure , two linear sections can be distinguished. The nonlinearity of the plot is an indicative of the differences of the thermodynamic processes, and it happens as a result of conformational changes of the analyte, the stationary phase or as a consequence of their interaction (Lao, ).…”

A review of retention mechanism studies for packed column supercritical fluid chromatography

“…Additionally, TM usually limits in providing physical chemistry information and in general rarely applied in practical separation science 10 . Hence, ETM is further used to establish the empirical correlation between thermodynamic parameters with the molecular structures, chromatographic conditions, and enthalpy‐entropy compensation 10,142 . Some ETM based on the quantitative structure–retention relationships (QSRR), which employ the molecular descriptors that well reflect physicochemical properties of a representative compound group to establish the relationship between compound properties and chromatographic retention data of these compounds 61 .…”

“… 10 Hence, ETM is further used to establish the empirical correlation between thermodynamic parameters with the molecular structures, chromatographic conditions, and enthalpy‐entropy compensation. 10 , 142 Some ETM based on the quantitative structure–retention relationships (QSRR), which employ the molecular descriptors that well reflect physicochemical properties of a representative compound group to establish the relationship between compound properties and chromatographic retention data of these compounds. 61 To obtain reliable QSRR models, choosing suitable parameters is important, and a strict statistical analysis must be proceeded.…”