Benzoic acid, 2-[[2-amino-6-[[4'-[[5-[(2,5-disulfophenyl)azo]-1-hydroxy-6-(phenylamino)-3-sulfo-2-naphthalenyl]azo]-3,3'-dimethoxy[1,1'-biphenyl]-4-yl]azo]-5-hydroxy-7-sulfo-1-naphthalenyl]azo]-5-nitro-, tetrasodium salt