1,2-dihydro-6-hydroxy-1,4-dimethyl-2-oxo-5-[[4-[[2-(sulphooxy)ethyl]sulphonyl]phenyl]azo]pyridine-3-sulphonic acid, sodium salt

1,2-Dihydro-6-hydroxy-1,4-dimethyl-2-oxo-5-[[4-[[2-(sulfooxy)ethyl]sulfonyl]phenyl]azo]-3-pyridinesulfonic acid/sodium,(1:x) salt