2,7-Naphthalenedisulfonic acid, 5-[[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]-4-hydroxy-3-[2-(1-sulfo-2-naphthalenyl)diazenyl]-, sodium salt (1:?)