Reproducibility, accuracy, and correction of isotherm data measured by chromatography

Abstract

Using the methods of frontal analysis and elution by characteristics points, the isotherm of 3-phenyl-1-propanol was determined on four commercially available 10-μm ODS C 18 packing materials: KROMASIL, VYDAC, YMC and ZORBAX. Each stationary phase was packed into five 10×0.46 cm I.D. columns. A methanol-water mixture (45:55, v/v) was used as the mobile phase and solvent. The column efficiencies and capacity factors were also determined for a series of compounds: m-cresol, benzyl alcohol, methyl benzoate, benzyl acetate, 2-isopropylphenol, and 2,6-dimethylphenol, all eluted under infinite dilution conditions. The average total column porosities were derived from the uracil retention volume, the internal and external porosities by reversed size-exclusion chromatography. Different columns packed with material from the same lot have significantly different thermodynamic properties. Corrections of isotherm data based on the difference between column retention factors and phase ratios do not compensate correctly for the deviations observed but corrections based on the difference of external porosites of the column do.