Determination of heats of vaporization and gibbs free energies of alkylbenzenes on GC stationary phases of different polarity

Abstract

Summary In our paper we propose a new method for the determination of heats of vaporization (Anvap(i)) and the Gibbs free energies of vaporization (Ap.p(i)) for individually selected alkylbenzenes, chromatographed on stationary phases of low and medium polarity. The method is based on a new thermodynamic description of the Ko%ts retention index (I(i)) making use of Trouton's rule. In fact, we attribute physical significance to two empirical relationships, well known from the literature. We can describe thermodynamically the magnitude of I(i) using two relations, each of them potentially useful for further determination of Anvap(i) and A~p(i ). A comparison was made of the results obtained with the use of our new approach and of those already existing in the literature attained in a completely different way. The comparison suggests that the calculated AHvap(i) and Al.tp(i) values are thermodynamically acceptable and hence correct, and the data suit into the series of similar values determined on stationary phases of different polarity.