PURPOSE:To stabilize and solubilize a diazonium compound in an essential element of analysis against and in an aqueous solution for coating, by using high molecular carboxylic acid combined with a nonionic surface active agent as a binder. CONSTITUTION:High molecular carboxylic acid combined with a nonionic surface active agent via ester combination in at least a part of carboxyl radical containing in its molecule is used for this essential element of analysis as a binder instead of a simple high molecular carboxylic acid. Thereby, not only the stabilization of the unstable diazonium compound in the essential element of the analysis is attained but the solubility of the diazonium compound having a hydrophobic radical in an aqueous solvent under the coexistence of this binder is improved. Accordingly, the generation of phenomena such as deposition of the diazonium compound in the coating solution and stratified structure such as a formed coloring reaction layer is prevented effectively.
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