An ink composition comprising: a betaine-based surfactant represented by the following general formula (1) and a linear saturated aliphatic alcohol having a hydroxyl value of 1 to 2 and 4 to 6 carbon atoms: [C 1](R).sub.p--N-[L-(COOM).sub.q].sub.r Formula (1) (wherein, R represents a hydrogen atom, alkyl group, aryl group or heterocyclic group, L represents a divalent or more linking group, M represents a hydrogen atom, alkaline metal atom, ammonium group, protonated organic amine or nitrogen-containing heterocyclic group or quaternary ammonium ion group, or represents a group that does not exist as a cation in the case of being a counter ion of an ammonium ion formed of an N atom in formula (1), q represents an integer of 1 or more, r represents an integer of 1 to 4, p represents an integer of 0 to 4, p+r is 3 or 4, N is a nitrogen atom that composes a quaternary amine in the case p+r is 4, R may be the same or different when p is 2 or more, COOM may be the same or different when q is 2 or more, and L-(COOM).sub.q may be the same or different when r is 2 or more).

 
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> Physically crosslinked copolymer compounds and related compositions and methods for electrophoretic separation

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