1,7-Naphthalenedisulfonic acid, 2-[[4-fluoro-6-[methyl[2-[[2-(sulfooxy)ethyl]sulfonyl]ethyl]amino]-1,3,5-triazin-2-yl]amino]-5-hydroxy-6-[2-(4-methyl-2-sulfophenyl)diazenyl]-, sodium salt (1:?)