Fig. 2. High performance liquid chromatography profiles with electrochemical detection of erythromycin A (initial concentration, 200 µg mL^–1) and the degradation products from (A) the degradation in water for 72 h at 25°C, (B) the 10-min equilibration in H⁺–exchanged montmorillonite suspension (solid to solution ratio = 1:100), (C) the 24-h degradation by H⁺–exchanged montmorillonite, and (D) the 24-h degradation by Fe³⁺–exchanged montmorillonite. One-microampere current signals are marked at 0 and 2 min.