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Temperature dependence of kováts indices in gas chromatography. Explanation of empirical constants by use of transition-state theory

Kowalska T., Héberger K., Görgényi M.

Acta Chromatographica

2003

No. 13

60-68

The temperature dependence of Kováts indices is best described by use of the empirical equation I = A + B/T + C lnT [1]. This paper discusses the physical significance of the equation constants linked to the 1/T and lnT terms. The explanation presented here is based on transition state theory, i.e. the activation energy assumed to be associated with the solvation process. Because the literature contains no measured activation energy data for the solvation process, elucidation of the physical meaning of other terms might be an acceptable alternative. The Gibbs free energy for one methylene unit can be calculated and compared with literature values. The activation energy of the solvation process changes systematically.

Determination of the Gibbs free energy of one methylene unit from Kováts retention index-boiling point correlations on DB-210 stationary phase

Héberger K., Kowalska T., Görgényi M.

Acta Chromatographica

1999

No. 9

25-37

A novel linear relationship has been derived, by use of the extension of Trouton's rule (i.e. the Trouton-Hildebrand-Everett rule), to describe the correlation between Kováts retention indices (I(i)) and boiling point (TB(i)). This thermodynamically based relationship applies to the retention of low-polarity solutes on low-polarity stationary phases. It can also be used for simple correlation between I(i) and TB(i), enabling prediction of the retention parameter (i.e. I(i)) for members of a congeneric set of solutes from their respective boiling points only. This new relationship can, however, also be used in an alternative and simple way of determining the Gibbs free energy of vaporization of one methylene group (CH2) of n-alkanes (Δμp(CH2)). The performance of the new relationship in purely statistical terms and also in the evaluation of numerical values of the magnitude (Δμp(CH2)) was assessed by comparison of retention data with literature values for selected carbonyl compounds, i.e. for certain aliphatic aldehydes and ketones, on four stationary phases of different polarity.