Definition: A family of spiro(isobenzofuran-1(3H),9'-(9H)xanthen)-3-one derivatives. These are used as dyes, as indicators for various metals, and as fluorescent labels in immunoassays.
6-carboxyfluorescein [ 5(6)-carboxyfluorescein,carboxyfluorescein ] originally sold as 6-carboxyfluorescein, but commercial product is a mixture of two isomers; correct name is 5(6)-carboxyfluorescein