Preservative composition for biological samples

A preservative composition, comprising a zwitterion polymer of the following formula (1) or a labeled form thereof:

• wherein
• X1 and X2 are the same or different and each represent a carbon atom or a nitrogen atom;
• Y1 and Y2 are the same or different and each represent an anion selected from the group consisting of —COO−, —SO3−, —OP═O(H)O−, —OP═O(CH3)O−, and —OP═O(OR1)O−;
• Z represents a hydrogen atom, an optionally alkyl group-substituted aromatic hydrocarbon group having 6 to 10 carbon atoms, an optionally alkyl group-substituted 5- or 6-membered aromatic heterocyclic group, an optionally alkyl group-substituted nitrogen-containing heterocyclic ammonium salt, a tetraalkylammonium salt, a tetraphenylphosphonium salt, a tetraalkylphosphonium salt, a trialkylsulfonium salt, or a linear or branched alkyl group having 1 to 22 carbon atoms and optionally having 1 to 3 oxygen atoms in a molecular chain;
• e and f each represent an integer of 0 or 1;
• l, m, and n are each a number which indicates a content ratio of each repeat unit and represent a number which satisfies 0<l≤1, 0≤m<1, 0≤n<1, and 1+m+n=1;
• and
• p, q, r, s, and t each represent an integer of 0 to 6.