The Impact of Water as an Additive on the Elution of Some Basic Organic Compounds in Supercritical Fluid Chromatography.

In this study, water was used as an additive in the methanol-modified carbon dioxide-based eluent for the elution of some basic organic compounds from a hybrid silica column via supercritical fluid chromatography (SFC). The experiments were applied to sulfonamides, propranolol, and other organic nitrogen compounds involving aromatic rings from different classes of amine, pyrimidine, and purine with different pKa values (the pKa values for the studied analytes range from 4.6 to 10.

The adsorption of methanol on reversed phase stationary phases in supercritical fluid chromatography.

The surface excess isotherms of methanol from carbon dioxide on reversed phase stationary phases under two different operational conditions - which can be considered subcritical and supercritical conditions depending on the molar fraction of CO in methanol - were determined using the minor disturbance peak method. The shapes of the surface excess isotherms were very similar in subcritical and supercritical conditions for the same column. To verify the influence of the sample solvent on the separation efficiency, two solvents methanol and heptane were used as sample solvents for alkylbenzene samples for the separation on the studied columns with pure carbon dioxide mobile phase.