3',6'-Dihydroxy-3-oxospiro(isobenzofuran-1(3H),9'-(9H)xanthene)-5,6-dicarboxylic acid 5,6-Dicarboxyfluorescein 90829-94-0 Spiro(isobenzofuran-1(3H),9'-(9H)xanthene)-5,6-dicarboxylic acid, 3',6'-dihydroxy-3-oxo-