2,7-Naphthalenedisulfonic acid, 4-hydroxy-5-[[4-[[4-[(2-hydroxyethyl)amino]-6-[[5-hydroxy-6-[(2-methoxy-5-sulfophenyl)azo]-7-sulfo-2-naphthalenyl]amino]-1,3,5-triazin-2-yl]amino]-5-methoxy-2-methylphenyl]azo]-, monosodium salt