Empirical Formula (Hill Notation): C20H10Na2O5, Molecular Weight: 376.27, used as fluorescent tracer, Synonym: Acid Yellow 73, D&C;Yellow No. 8, NaFl, NaFluo, Sodium fluorescein, Uranine. Fluorescein sodium salt has been used as a solute to study microvessel permeability. It has been used as a test molecule to study blood barrier penetration.