Alkali Metal Ion Sensing in Aqueous Media by a Dibenzo-16-crown-5 Chromoionophore

Abstract

A new chromoionophore sym-(decyl)(2-hydroxy-5-nitrobenzyloxy)-dibenzo-16-crown-5 (1) has been synthesized for Na+ photometry in aqueous media. Apparent pKa values of 1 in the presence of 0.10 M LiCl, NaCl, and KCl were measured by spectrophotometry in 50% 1,4-dioxane-50% water (v/v) and compared with the pKa of 8.68 in the presence of 0.10 M TMACl. A significant pKa shift to a lower pH was only observed for Na+ (ΔpH=131) due to selective binding of 1 with Na+. Based upon this pKa shift, chromoionophore 1 was found to selectively respond to Na+ with a detection limit of 10^(−3)M and no interference from K+ up to 0.05 M for detection of 10.0 mM Na+ in 50% 1,4-dioxane-50% water (v/v).