One-Pot Synthesis of Hantzsch Reaction for Fluorometric Quantification of Epinastine in Aqueous Humor Samples

Epinastine (EPS), an antihistaminic drug, is used to prevent itching of the eye caused by a condition known as allergic conjunctivitis. Few reported methods were reported for detecting EPS. Most of these reported methods are chromatographic methods that require expensive techniques and hazardous solvents. Inspired by EPS's medical importance and the absence of native fluorescence of ESP, we introduce a sensitive fluorimetric method for detecting EPS in eye drops and artificial aqueous humor for the first time. The method presented here utilizes a well-known derivatization reaction called Hantzsch derivatization reaction to convert the nonfluorescent EPS drug to a fluorescent derivative. All the factors affecting the sensitivity of the developed method were optimized to enhance the method's sensitivity. After optimizations, this reaction enables the fluorimetric quantification of EPS at λ_em 484 nm (λ_ex = 410 nm) in eye drops and spiked aqueous humor without any interference from the excipients or naturally present biomolecules. The dynamic range for EPS detection in the pure state is 0.1–1.0 μg/mL (LOQ = 79.23 ng/mL and LOD = 26.15 ng/mL). The approach exhibits favorable percentage recoveries in spiked aqueous humor (95.80 ± 1.57% to 100.80 ± 1.89%).