Polar-bonded stationary phases, such as CN-, diol- and NH2-silica, have been characterised by the retention of model solutes (phenols, aromatic amines and quinoline bases) in normal-phase systems using n-heptane--polar modifier (2-propanol, tetrahydrofuran or dioxane) mixtures as eluents. The selectivity of separation for the particular groups of substances has been analysed by the log kI versus log kII relationships for CN- and diol, CN- and NH2- and NH2- and diol phases in examined eluent systems by the plotting of correlation lines. The values of regression coefficient r indicate either the similarity of the retention mechanisms of model solutes in some examined systems where r>0.9, or differences among various systems where r<<0.9. The values of slopes of correlation lines show the selectivity of separation for particular group of compounds. The selectivity of separation has also been characterised by deltalog k values. The effect of modifier (2-propanol, tetrahydrofuran and dioxane) on selectivity of model solutes on these phases has also been discussed.