Empirical correlations between gas-chromatographic retention data and physical or topological properties of solute molecules

Kováts retention indices (I) and relative retention times (τ) using Silicone oil 550 or Bentone 34 as the stationary phase were measured for 20 hydrocarbons (mainly alkylbenzenes). Statistical analysis of repeated determinations indicated that the empirical distribution function of retention indices is not normal; the relative standard deviations decrease with increasing retention index. Several models were examined to describe the retention data as a function of boiling point (T_B) and molar refraction, molar volume, connectivity indices, etc. A universal fitting equation y_i=A exp (BT_Bi) + Cx_2i + D (where y_i=I or τ, and x_2i is one of the properties mentioned) proved to be best on the basis of statistical characteristics (examination of residuals, multiple correlation coefficient, residual mean square, variance ratio tests) which were also evaluated. The results were compared to equations recommended in the literature.