A Study of the Dependence of the Kováts Retention Index on the Temperature of Analysis on Stationary Phases of Different Polarity

The dependence of Kováts retention indices on the temperature of GC analysis is not always regular. In some chromatographic systems this dependence is characterized by a readily perceptible minimum [1–3]. To monitor this type of relationship a set of test compounds was selected from among the aldehydes, ketones, and alkylbenzenes and their gas chromatographic behaviour was studied on stationary phases of different polarity and over a wide range of working temperatures. For some systems we observed a minimum on the plot of I against Tc. This minimum was not only observed, it was also computationally confirmed by use of the equation I = A + B/Tc + ClnTc, where A, B, and C are terms of the equation with physicochemical significance [2,4–6]. On the basis of this equation we were also able to evaluate two thermodynamic magnitudes, the activation enthalpy, ∆H, and the chemical potential of the partitioning of one methylene group between the two phases of the chromatographic system, ∆μp(CH2), for all the analytes investigated.