Biparameter Equations for Calculating Kovats Retention Indices of Hydrocarbons

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Abstract
Biparameter equations, in which one parameter is the boiling point of the solutes and the other is any of their physicochemical properties able to account for dispersive solute-stationary phase interactions, are obtained by regression analysis. These equations permit the calculation of Kovats retention index (IR ) for aliphatic and aromatic hydrocarbons in complex mixtures with standard deviations close to experimental error. The linear change of regression coefficients with the work temperature allow us to obtain equations suitable for calculating IR at any temperature on a given stationary phase. Furthermore, accurate values for the magnitudes included in the equations can be obtained starting from IR values. When alkylbenzenes are separated on polar phases, such as Carbowax 20M, it is necessary to add a new parameter accounting for inductive interactions. Once again, regression coefficients, except that of the boiling point which remains constant, change linearly with the polarity of the phase (Tarjan's scale) enabling the obtaining of an equation for calculating IR on any stationary phase at a given work temperature, although constant deviations between calculated and experimental IR , on polymeric stationary phases, are found.