FIGURE 5.

Theoretical and Experimental Validation of Sensor Working Principle. (A) pH values of various NaOH solutions were theoretically calculated across the %CO₂ working range (gray box). The pKa of HPTS is 7.7, and can be seen as the horizontal green line. (B) Solutions containing 50% glycerol have significantly lower pH than the corresponding solutions without glycerol. (C) The theoretical (green squares) and measured (red circles) sensitivity (or pH gradient change, m) under different base conditions. In each case, above a certain base concentration, change in pH reached a maximum. Solutions containing 50% glycerol reached a maximum at a higher base concentration, resulting from reduced pH values.