DISCUSSION OF DECREASE IN HOMOLOGOUS RETENTION INCREMENT ON RAISING POLARITY OF A STATIONARY PHASE IN GAS-CHROMATOGRAPHY

The empirical observation that the retention ratio of two successive homologues decreases upon increasing the polarity of the stationary phase in gas chromatography is explained in terms of the thermodynamic properties of the sorption system. This retention ratio is proportional to the negative value of the sum of the standard Gibbs free energy change of condensation and the partial excess Gibbs free energy per mole of a CH2 group of the solute. As the value of the Gibbs free energy of condensation is negative while the excess Gibbs free energy increases in the positive direction on increasing the polarity of the sorbent, the absolute value of the above sum must be. the smaller, the higher the polarity of the sorbent. © Elsevier Scientific Publishing Company, Amsterdam.