PROPERTIES OF SOME C-18 STATIONARY PHASES FOR PREPARATIVE LIQUID-CHROMATOGRAPHY .1. EQUILIBRIUM ISOTHERMS

Isotherm data were measured by frontal analysis and elution by characteristic points for 2,6-dimethylphenol, 3-phenyl-1-propanol and methyl benzoate on six columns packed with two commercial octadecyl silicas, using methanol-water solutions as the mobile phase. The retention factors and isotherm coefficients depend on the packing density. This density varies markedly from column to column, at least with some phases for which it is also a function of the column length. The determination pf the thermodynamic data required for the modelling of chromatography must be done with an accuracy which seems to exceed what the current level of column to column reproducibility of these data permits at present, even when care is taken to control the experimental parameters, make precise measurements and report the data to the mass of silica.