THERMO-OXIDATIVE DECOMPOSITION ANALYSIS OF LEVOFLOXACIN BY ISOCONVERSIONAL KINETICS AND COMPUTATIONAL METHODS

Abstract

This study presents a thorough thermogravimetric analysis (TGA) to comprehend the thermal decompaction of the antibiotic drug levofloxacin, as a model pharmaceutical pollutant. The reaction was analyzed under N2 gas flow using a TGA analyzer at different heating rates. The isoconversional methods of Kissinger–Akahira–Sunose (KAS) and Friedman were applied to obtain the effective activation energy (Eα) of the decomposition as a function of the extent of conversion (α). The Eα of levofloxacin’s decomposition reaction was found to be between 23.3 – 68.5 kJ/mol for the KAS method, and between 48.3 – 117.5 kJ/mol for the Friedman method, positively correlating to α. Additionally, Differential scanning calorimetry (DSC) was used to assess the thermodynamic physical and chemical changes that occur as a function of temperature. And Density functional theory (DFT) calculations were used to calculate the bond dissociation energies (BDEs) of the levofloxacin possible degradation routes. The DFT analysis along with DSC and Friedman method’s results suggest that the most probable dissociation route is aromatic-Me bond to give off •CH3 radicals.