Frontal elution profiles 0.75 μM etoposide (A), 5 μM etoposide (B), 0.75 μM etoposide + 2 μM verapamil (C), 5 μM etoposide + 2 μM verapamil (D), on the NMAC (LN-229)-IAM column (0.531 cm × 2 cm) on the Agilent LC–MSD by frontal affinity chromatography using ammonium acetate [10 mM, pH 7.4] at 0.4 ml min−1 as the mobile phase.