tetrasodium 4-hydroxy-3-[(1-sulphonato-2-naphthyl)azo]-5-[[[[3-[[2-(sulphonatothio)ethyl]sulphonyl]phenyl]amino]carbonyl]amino]naphthalene-2,7-disulphonate

4-Hydroxy-3-[(1-sodiooxysulfonyl-2-naphthalenyl)azo]-5-[[[[3-[[2-(sodiooxysulfonylthio)ethyl]sulfonyl]phenyl]amino]carbonyl]amino]-2,7-naphthalenedisulfonic acid disodium salt