Thermodynamic explanation of separations of enantiomeric mixtures using polysaccharide based chiral stationary phases in HPLC

Author: Aluda Chelidze
Co-authors: giorgi kobidze, gizo dolidze
Keywords: Enantiomers, Thermodinamic parameters, temperature influence
Annotation:

For the experiment 28 acidic compounds were chosen, particularly arylpropionic acid derivatives, which are nonsteroidal anti-inflammatory drugs (NSIDs). They are used as painkillers and antipyretics. It is important to separate their stereoisomers, as frequently only one enantiomer has pharmacological activity and the other one is inactive or even toxic. From these compounds we selected fenoprofen and ketoprofen for detailed thermodynamic studies. The goal of our research was the calculation of thermodynamic parameters of enantioseparation in high-performance liquid chromatography. This can help to predict the suitable analytical conditions for the given compound on given column for achieving the desired selectivity and enantiomer elution order. Also we compared thermodynamic parameters using amylose tris(3,5-dimethylphenyl carbamate) coated on silica gel as stationary phase. Separation of enantiomers was performed at different temperatures and in different mobile phases. For analyzed compounds, the difference in adsorption enthalpy and adsorption entropy between enantiomers were calculated using the plot of natural logarithm of the separation factor versus the reciprocal of the absolute temperature. We studied if the enantioseparation mechanism was controlled by enthalpic or entropic terms and what was the influence of temperature on retention and separation. The results of this study have shown that temperature significantly affects chiral recognition pattern of polysaccharide phenylcarbamates. The question is if the change of chiral recognition pattern is caused by any chemical or structural change in the chiral selector, chiral analyte, both of them or, it is the result of enthalpy-entropy compensation. In order to get some idea on this regard, the enantioseparation of ketoprofen was studiedon Lux Amylose-1 column in the temperature range 10-70°C when increasing the column temperature with 5° increments and afterwards, when cooling of the same column with the same increments down to 10°C.