Investigation of the effect of mobile phase composition on selectivity using a solvent-triangle based approach in achiral SFC

Defining a method development methodology for achiral drug impurity profiling in SFC requires a number of steps. Initially, diverse stationary phases are characterized and a small number of orthogonal or dissimilar phases are selected for further method development. In this paper, we focus on a next step which is the investigation of the modifier composition on chromatographic selectivity. A solvent-triangle based approach is used in which blends of organic solvents, mainly ethanol (EtOH), propanol (PrOH), acetonitrile (ACN) and tetrahydrofuran (THF) mixed with methanol (MeOH) are tested as modifiers on six dissimilar stationary phases. The tested modifier blends were composed to have equal eluotropic strengths as calculated on bare silica. The modifier leads to minor changes in terms of elution order, retention and mixture resolution. However, varying only the modifier composition on a given stationary phase does not lead to the creation of dissimilar systems. Therefore the modifier composition is an optimization parameter, with the stationary phase being the factor determining most the selectivity of a given mixture in achiral SFC.