Spectrophotometric determination of levofloxacin using bromophenol blue: insight into the structure of the formed supramolecular complex.

Levofloxacin was determined using a spectrophotometric method based on the formation of a hydrogen-bonded supramolecular complex with bromophenol blue. The method was linear over 1-20 µg mL-1, with a limit of detection of 0.39 µg mL-1. It was successfully applied to commercial tablet formulations (250, 500, and 750 mg), yielding recoveries of 98.80-100.69%. Interference studies confirmed high selectivity toward common pharmaceutical excipients with recoveries ranging from 97.50-101.48% and RSD values below 1.57%. Greenness assessment using AGREE, Eco-scale, and White Analytical Chemistry (WAC) metrics demonstrated good environmental compatibility. Quantum chemical calculations were performed to get an insight into the nature of the formed supramolecular complex. The optimized structure demonstrated that two inter- and intramolecular hydrogen bonds stabilize the formed complex. NBO analysis confirmed the presence of charge transfer between levofloxacin and bromophenol blue via the carboxylic acid of the drug and one of the phenolic groups of bromophenol blue.