6'-Hydroxy-3-oxospiro(isobenzofuran-1(3H),9'-(9H)xanthen)-3'-yl 4-((aminoiminomethyl)amino)benzoate monohydrochloride 83616-10-8 Benzoic acid, 4-((aminoiminomethyl)amino)-, 6'-hydroxy-3-oxospiro(isobenzofuran-1(3H),9'-(9H)xanthen)-3'-yl ester, monohydrochloride Fluorescein mono-p-guanidinobenzoate Fmgb-hcl