Eco-friendly spectrofluorimetric determination of fenbendazole in pharmaceutical, plasma, and milk samples using erythrosine B as a fluorescent probe.

A simple, sensitive, and sustainable spectrofluorimetric method was developed to determine fenbendazole (FEN) based on its fluorescence-quenching interaction with erythrosine B (EB). Under the optimized conditions, FEN efficiently quenched the native fluorescence of EB (λ ex = 527 nm, λ em = 544 nm). The decrease in fluorescence intensity was proportional to FEN concentration over 0.050-3.0 µg mL-1 (r 2 = 0.9997), with limits of detection and quantification of 0.014 and 0.043 µg mL-1, respectively. Stern-Volmer analysis, thermodynamic studies, Job's method, spectral analysis, and quantum-chemical calculations collectively supported a predominantly static quenching mechanism involving a spontaneous 1 : 1 ground-state EB-FEN complex, with electrostatic interactions, hydrogen bonding, and partial charge transfer contributing to the interaction. The method was validated according to ICH Q2(R2) guidelines and showed satisfactory accuracy, precision, robustness, and selectivity for FEN determination in pharmaceutical formulations and spiked bovine plasma and milk samples following sample pretreatment. The sustainability of the proposed method was evaluated using AGREEprep, ComplexMoGAPI, CaFRI, BAGI, and RGB12, showing favorable environmental performance while acknowledging the acetonitrile used during plasma pretreatment. Because of its simplicity, speed, low solvent consumption, and modest instrumental requirements, the proposed method offers a practical complement to chromatographic methods for routine FEN determination in pharmaceutical formulations and spiked biological matrices.