| http://www.w3.org/ns/prov#value | - An ion sensor according to claim 3, wherein said hydrogen ion carrier substance is at least one member selected from the group consisting of amines represented by: ##STR12## (wherein each of R1, R2 and R3 is an alkyl group, at least two of which are alkyl groups having 8 to 18 carbon atoms), and pyridine derivatives represented by: ##STR13## (wherein R4 is an alkyl group having 8 to 18 carbon atom
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