A Novel Green Spectrofluorimetric Approach for Memantine Quantification With Mechanistic Elucidation Through Quantum Mechanical Modeling and Green Analytical Chemistry Evaluation.

A novel, sustainable spectrofluorimetric method was developed for memantine determination using erythrosin B as a fluorescent probe, addressing critical analytical gaps in pharmaceutical quality control and environmental monitoring. The method exploits static fluorescence quenching through ground-state complex formation between protonated memantine and anionic erythrosin B. Initially, UV-Vis absorption spectroscopy revealed a significant hypochromic effect accompanied by a hypsochromic shift of 5 nm, with the absorption maximum shifting from 527 to 522 nm upon complex formation, while fluorescence studies demonstrated concentration-dependent quenching at 527 nm excitation and 553 nm emission wavelengths. Subsequently, temperature-dependent Stern-Volmer analysis yielded quenching constants decreasing from 6.22 × 105 to 4.47 × 105 mol L-1 (298-313 K), confirming the static quenching mechanism. Furthermore, Job's method established 2:1 memantine-to-erythrosin B stoichiometry, which was validated by quantum mechanical calculations revealing energetically favorable binding interactions. The developed method exhibited excellent analytical performance with a linear range of 0.02-2.0 μg/mL, a detection limit of 6.5 ng/mL, precision (%RSD < 2%), and accuracy (98.59%). Moreover, successful applications included pharmaceutical formulations and spiked environmental water samples, achieving quantitative recoveries ranging from 96% to 104% across different matrices. Finally, a comprehensive sustainability assessment demonstrated superior green credentials compared to conventional chromatographic approaches.