Patent ID: 8585781

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 a content of (b) the at least one azo compound is 1% by mass to 25% by mass: wherein, in formula (1), A represents a substituted phenyl group or a substituted or unsubstituted nitrogen-containing 5-membered heterocyclic group, 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 cyano group, Y 2 , Y 3 and Y 4 each independently represents a hydrogen atom or a monovalent substituent, Y 2 , Y 3 and Y 4 may be bonded to each other to form a ring, all of Y 2 , Y 3 and Y 4 do not represent a hydrogen atom 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.