Evaluation of Acetonitrile in Combination With Alcohols as Modifiers in Chiral Supercritical Fluid Chromatography

This study systematically investigated the effect of acetonitrile (ACN) in combination with alcohols as modifiers for chiral supercritical fluid chromatography (SFC) separations. The elution profiles of nine internal samples were evaluated using various ratios of ACN/methanol (MeOH) mixtures as the modifiers on four chiral columns. Eighty-three percent of the retention factors (k') exhibited an initial decrease followed by an upward trend as the ACN percentage increased, likely reflecting changes in hydrogen-bonding, dipole-dipole, and π-π interaction sites on the chiral stationary phases (CSPs). A broader set of compounds, including those with two and four isomers, was further screened using four different ACN/alcohol ratios (2:8, 5:5, 7:3, and 8:2). Compared to pure alcohol modifiers, the ACN/alcohol mixtures demonstrated complementary chiral recognition for compounds with two isomers, resulting in improved and unique separations. For some four-isomer compounds, ACN/alcohol mixtures resolved more isomers than pure alcohols. Additionally, adding 20% ACN to the MeOH modifier significantly improved productivity for late-eluting compounds by reducing cycle time, sharpening peak shape, and decreasing system pressure due to its lower viscosity.