High-acidity determination in salt-containing acids by optical sensors. The scope of a dual-transducer approach and the Hammett acidity function

摘要

A dual-transducer approach based on sol-gel optical sensors was recently reported to measure acid and salt concentrations, C-acid and C-salt, in concentrated aqueous LiCl-HCl, CaCl2-HCl, and AlCl3-HCl solutions (C-acid at 5-6 M; C-salt less than or equal to 2 M).(1) The scope of this new approach has been studied in salt-containing HCl solutions with C-acid at 2-9 M, and factors that influence sensor responses and accuracy have been investigated. A linear relationship between (partial derivativeA/partial derivativeC(salt))(Cacid) and (dA/dC(acid))(Csalt=0), which is the basis of this dual-transducer approach, was found to lead to an empirical linear relationship between (DeltaH(0))(Cacid) and (DeltaC(salt))(Cacid) (H-0: Hammett acidity function of the indicator encapsulated in the sensor). [References: 43]