High-Basicity Determination in Mixed Water−Alcohol Solutions by a Dual Optical Sensor Approach

The activity of NaOH is known to be significantly affected by the presence of an alcohol in aqueous solutions. A novel linear relationship between (∂A/∂C_alcohol) and C_base was found in the highly alkaline, mixed H₂O−ROH solutions (R = Me, Et, i-Pr). The use of this linear relationship led to a dual-transducer approach to decompose the optical signals of optical base sensors and to give base and alcohol concentrations in concentrated NaOH−H₂O−ROH solutions ([OH^-] = 0.05−3.6 M). The scope of the new dual-sensor approach was evaluated, and errors in C_base and C_alcohol were analyzed. The optical base sensors consist of sol−gel SiO₂−ZrO₂−organic polymer composites doped with high-pK_a indicators. The pK_as of the indicators encapsulated in the composite films were determined and found to be affected by the composition of the sol−gel composites.