Fig. 4. Mass chromatograms of m/z 558 from the liquid chromatography electrospray ionization tandem mass spectrometry (LC/ESI-MS) analyses of the H⁺–exchanged montmorillonite degradation products of (A) anhydroerythromycin A, (B) erythromycin A enol ether, and (C) erythromycin A.