Effect of the injection of water-containing diluents on band broadening in analytical supercritical fluid chromatography

In this study, the impact of introducing water in the sample solvent upon the injection in SFC is investigated. Adsorption of water on the stationary phase was indicated. Using a set of ten neutral test compounds and four ionizable test compounds, spread all along the co-solvent gradient, several parameters were scrutinized (i.e. water content in the sample diluent, nature of the sample diluent, nature of the co-solvent) in regards to peak broadening. From this systematic investigation, the competition for adsorption on the stationary phase between the analytes and the water molecules contained in the diluent was highlighted. The chromatographic peaks of neutral molecules eluting before water molecules were compressed and the ones eluting after were broadened. While the extent of this phenomenon was related to the peak position for neutral molecules, it was not observed on acidic molecules.