New Sensitive Derivatization Methodology of Levofloxacin Antibiotic from its Dosage Formulations: Kinetic Spectrophotometric Methods for Determination

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A modern validated kinetic spectrophotometric method with a novel coupling reagent has been described for the determination of levofloxacin (LEV) in pure and tablets. The method involves an oxidative-coupling reaction between LEV and 3-methyl-2-benzothiazolinone hydrazone hydrochloride monohydrate (MBTH), in the presence of Ce(IV) in H2SO4 medium at 25±1°C, to gives greenish-blue product. The reaction is followed spectrophotometrically by measuring the increase in absorbance with time at 629 nm and then is stable for more than 2 hrs. The initial rate, rate constant, fixed absorbance and fixed time methods have been tested for constructing the calibration graphs, and are linear. The most suitable analytical methods were the initial rate and fixed time (at 20 min) methods for determination of LEV in the concentration ranges of 2.0-35.0 μg mL-1 and 0.65-35.0 μg mL-1 with LOD is 0.422 and 0.074 μg mL-1, respectively. Molar absorptivity for the method was found to be 1.40×104 L mol-1 cm-1. The activation energy (E ), activation enthalpy (ΔH‡), activation entropy (ΔS‡) and Gibbs free energy (ΔG‡) are estimated for the reaction and found to be 9.84 KJ mol-1, 7.40 KJ mol-1, 177.04 JK-1 mol-1 and -44.48 KJ mol-1, respectively. The kinetic proposed methods were further applied to the determination of LEV in tablet formulations with no interfere from the excipients.