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. Author manuscript; available in PMC: 2015 May 1.
Published in final edited form as: Sens Actuators B Chem. 2014 Jan 18;195:171–176. doi: 10.1016/j.snb.2013.12.110

Figure 1.

Figure 1

Titration curves for the HCO3−/CO32− buffer system modified with thymol blue and m-cresol purple. The color changes in the CO2 sensor were due to the pKa value (for thymol blue: color changes from blue (pH > pKa) to yellow (pH < pKa); for m-cresol purple: color changes from purple (pH > pKa) to yellow (pH < pKa)). Compared with thymol blue, m-cresol purple changes color more sensitively under neutral to weakly alkaline conditions, which provides a larger dynamic range for the breath CO2 detection.