3-[6-[N-Ethyl-N-(p-methylsulfonylaminophenyl)carbamoyl]-5-hydroxy-8-(2-methylsulfonyl-4-nitrophenylazo)-1-naphtylaminosulfonyl]benzenesulfonic acid sodium salt

3-[[[6-[[Ethyl[4-[(methylsulfonyl)amino]phenyl]amino]carbonyl]-5-hydroxy-8-[[2-(methylsulfonyl)-4-nitrophenyl]azo]-1-naphthalenyl]amino]sulfonyl]benzenesulfonic acid sodium salt