Influence of sample solvent and stationary phase polarity on peak broadening, distortion and splitting due to the ‘flooding effect’

Abstract

Experimental data and rough theoretical calculations show that the residence time of liquid solvent inside a column is related to the amount of solvent vapours transported at equilibrium outside the column. The evaporation time is independent of the nature of the stationary phase. Liquid sample migration inside the column depends on the polarities of both the sample solvent and stationary phase. On non-polar immobilized stationary phases, highly polar solvents produce much larger flooded zones than non-polar ones. The dependence of column separating power on solvent polarity (mixtures of chloroform and methanol with different compositions) shows an S-shaped curve, suggesting a change of liquid migration mechanism for highly polar solvents. Visual observations support this conclusion. At column temperatures higher than the boiling point of the solvent these differences practically disappear. On polar immobilized stationary phases, similar wet zones are obtained for polar or non-polar solvents. Their lengths are similar to those obtained on non-polar stationary phases when non-polar or slightly polar solvents are used. However, peak-broadening, distortion and splitting phenomena are less evident, suggesting that the distribution of sample components along the flooded zone depends on the nature of the stationary phase.