Selective colorimetry of alkali metal ions in aqueous dioxane solution by calix[4]crown chromoionophore possessing three dimensionally designed ion recognition site has been examined. Based upon a tautomerism from phenylazophenol to quinone hydrazone structure by forming MHL complex, chromoionophore was found to show a selective color change for Na+ in acidic aqueous media. In the same condition, no response was observed for Li+, K+, and TMA+.
