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fluorescein fluo·res·ce·in (flu-rěs'ē-ĭn, flô-)
An orange-red compound that exhibits intense fluorescence in alkaline solution and is used in ophthalmology to reveal corneal lesions.
organic compound of molecular formula C20H12O5 that has wide use as a synthetic colouring agent. It is prepared by heating phthalic anhydride and resorcinol over a zinc catalyst, and it crystallizes as a deep red powder with a melting point in the range of 314 to 316 C (597 to 601 F). Fluorescein was named for the intense green fluorescence it imparts to alkaline solutions-a colour visible even at dilutions of 1:50,000,000. It is used as a dye to colour liquids in analytic instruments, in cosmetics, and as a water tracer or marker. Halogenated derivatives made from fluorescein also include eosin and erythrosin.