| http://www.w3.org/ns/prov#value | - When X is an aromatic sulfonic acid ion which may have a substituent, it is particularly preferably a benzenesulfonic acid ion or a naphthalenesulfonic acid ion, and examples of a substituent forthe benzenesulfonic acid ion include a C.sub.1 -C.sub.14 alkyl group, an amino group, a halogen atom or the like, and examples of a substituent for the naphthalenesulfonic acid ion include a hydroxyl group
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