3',6'-Dihydroxy-3-oxospiro(isobenzofuran-1(3H),9'-(9H)xanthene)-6-carboxylic acid 3301-79-9 6-Carboxyfluorescein Spiro(isobenzofuran-1(3H),9'-(9H)xanthene)-6-carboxylic acid, 3',6'-dihydroxy-3-oxo-