Temperature-Dependent Elution Behavior of Steroids on PNIPAAm Brush-Modified Silica Bead Columns: Effects of Methanol and Ethanol in Aqueous Mobile Phases

Poly(N-isopropylacrylamide) (PNIPAAm) brush-modified bead-packed columns have been investigated as temperature-responsive stationary phases. However, these columns often exhibit long analyte retention times. In this study, methanol or ethanol was added to the mobile phase to investigate its effect on analyte elution behavior in a PNIPAAm brush-modified bead-packed column. The phase transition temperature of PNIPAAm decreased with the addition of methanol or ethanol, due to enhanced dehydration of the polymer. The temperature-dependent elution of steroids was examined using a PNIPAAm brush-modified silica bead-packed column with aqueous mobile phases containing methanol or ethanol. The retention times of steroids decreased with the addition of these organic solvents, likely because of increased solubility in the mobile phase. Ethanol reduced retention times more effectively than methanol. These results demonstrate that the addition of methanol or ethanol to the mobile phase is an effective approach for controlling analyte retention in PNIPAAm brush-modified silica bead-packed columns.