When using an alkaline eluent with a higher pH than the pKa sample value, basic drug components which have tertiary amino groups can be retained by the column because the amino groups are not dissociated and, in consequence, the hydrophilicity of the drug components decrease. Such analysis conditions can be realized for Asahipak ODP-50 columns because they can be used at pH11.


Sample : 1. Benzocaine, 2. Lidocaine, 3. Tetracaine hydrochloride

Column       : Shodex Asahipak ODP-50 4D (4.6 mm I.D. x 150 mm)
Eluent       : 25 mM Phosphate buffer/CH3CN=60/40
Flow rate    : 0.6 mL/min
Detector     : UV (254 nm)
Column temp. : 30 °C