1,3,6-Naphthalenetrisulfonic acid, 7-[2-[2-[(aminocarbonyl)amino]-4-[[4-[[5-amino-4-sulfo-2-[2-[4-[[2-(sulfooxy)ethyl]sulfonyl]phenyl]diazenyl]phenyl]amino]-6-chloro-1,3,5-triazin-2-yl]amino]phenyl]diazenyl]-, sodium salt (1:?)