Temperature dependence of the free energy of sorption ofn-alkanes and energy contribution of their methylene groups on columns with fullerene C60
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The partial molar free energy, enthalpy, and entropy of sorption of C11−C23 n-alkanes were calculated on the basis of the GC data obtained on the glass capillary column coated with fullerene C60 (Ful-60) as stationary phase. The thermodynamic parameters ofn-alkane sorption on a column with Ful-60 and a fused silica capillary column with polydimethylsiloxane OV-1 were determined and compared. The enthalpy-entropy compensation effect for the sorption ofn-alkanes on Ful-60 and OV-1 was found. A linear dependence of the partial molar free energy ofn-alkane sorption on the temperature of analysis and carbon chain length was found. The free energy contributions of the methylene groups were calculated, and their temperature dependences were studied. The differences in the temperature dependences of the energy contributions of methylene groups ofn-alkanes on Ful-60 and OV-1 were revealed. The entropy contribution is 68–82% of the enthalpy contribution which indicates a substantial role of the number of contacts with Ful-60 in retention ofn-alkanes. The ability of Ful-60 for dispersive interactions is similar to those of nonpolar liquid phases and substantially differs from that for carbon adsorbents. Fullerene columns were shown to be convenient for analysis of highly boiling organic substances in aqueous and organic solutions.
Key wordscapillary gas chromatography fullerene C60 as stationary phase n-alkanes partial molar free energy of sorption enthalpy entropy energy contribution of methylene group temperature dependence
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