title: Temperature dependence of Kováts indices in gas chromatography revisited.
abstract: Temperature dependence of the Kováts retention index (I) was measured for some aliphatic ketones and aldehydes on a poly(dimethyl siloxane) (HP-1) stationary phase. An interesting minimum (non-linearity) was observed for the I versus isothermal column temperature (T) relationships. A novel empirical model is proposed: I=A+B/T+C ln T, where A, B and Care equation constants and B/C = T(min). A detailed statistical analysis clearly shows superiority of the extended model (i.e., of this containing the logarithm of the temperature (ln T) term) over the earlier established Antoine-type reciprocal equation. The minimum temperature (and the energy like quantity=RT(min), where R is the gas constant) changes in a systematic manner. The factors effecting the (RT(min)) term are as follows: (i) this term decreases with the increase of the molecular mass of the respective oxo compounds; (ii) ketones have higher absolute values of (RT(min) than aldehydes; (iii) branching of the carbon chain lowers the mentioned (RT(min)). This enthalpy term is unambiguously bound to the polarity of solutes.
authors.affiliation: Institute of Chemistry, Chemical Research Center, Hungarian Academy of Sciences, Budapest. heberger@chemres.hu
authors.forename: Károly
authors.initials: K
authors.lastname: Héberger
authors.forename: Miklós
authors.initials: M
authors.lastname: Görgényi
authors.forename: Teresa
authors.initials: T
authors.lastname: Kowalska
mesh_terms: D002849:Chromatography, Gas / Q000379:methods*; D015203:Reproducibility of Results; D013696:Temperature