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Adsorption and Clay-Catalyzed Degradation of Erythromycin A on Homoionic Clays

Yong-Hak Kim, Thomas M. Heinze, Seong-Jae Kim and Carl E. Cerniglia*

Div. of Chemistry, National Center for Toxicological Research, U.S. Food and Drug Admin., Jefferson, AR 72079



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  		Fig. 1. Adsorption of erythromycin A on homoionic clays with a solid to solution ratio of 1:100 for kaolinite (K) and 1:500 for montmorillonite (M). The adsorption isotherms at 10°C (solid circles) and 25°C (open circles) are fitted to the Freundlich equation with unbroken line curves and broken line curves, respectively.

 


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  		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.

 


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  		Fig. 3. Mass chromatograms of m/z 540 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.

 


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  		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.

 


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  		Fig. 5. Molecular structures of erythromycin A and its degradation products.

 


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  		Fig. 6. Proposed degradation pathways of erythromycin A by the acid and clay catalysis.

 




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