Optical Sensors and the Salt Effect: A Dual-Transducer Approach to Acidity Determination in a Salt-Containing Concentrated Strong Acid

Abstract

A dual-transducer approach has been developed to decompose the optical signals of acid sensors in salt-containing concentrated acid solutions and to give acid and salt concentrations in concentrated LiCl-HCl, CaCl2-HCl, and AICl3-HCl solutions, respectively. The optical acid sensors in this approach are films of porous sol-gel SiO2 or SiO2-Nafion composite doped with low-pKa indicators. A novel linear relationship (dA/dCsalt)cCacid = beta x (dA0/dCacid)Csalt = 0 (A = absorbance of the sensor in a salt-containing HCl solution; A0 = absorbance of the sensor in a salt-free acid solution) was found, and the current approach is based on a set of nonlinear equations derived from this relationship.