Patent ID: 8603191

Claim:
An aqueous solution comprising: (a) a preservative; and (b) at least one azo compound represented by the following Formula (1) or a salt thereof, wherein the content of (b) is 1% by mass to 25% by mass: wherein, in Formula (1), G represents a nitrogen atom or —C(R 2 )═, R 2 represents a hydrogen atom, a sulfo group, a carboxy group, a substituted or unsubstituted carbamoyl group or a cyano group, X 1 , X 2 , X 3 , X 4 , X 5 , X 6 and X 7 each independently represents a hydrogen atom or a monovalent substituent, Y 2 , Y 3 and Y 4 each independently represents a hydrogen atom or a monovalent substituent, and may be bonded with each other to form a ring, provided that all of Y 2 , Y 3 and Y 4 do not represent hydrogen atoms at the same time, and M each independently represents a hydrogen atom or a monovalent countercation, and at least one M is a lithium ion.