Real-Time Measurement of pH in Atmospheric and Pressurized Systems Using a Low-Cost Image Analysis Method

The pH is an important parameter to control in many industrial processes carried out at high pressures. However, the measurement of pH in pressurized systems is challenging due to the difficulty in the development of pH sensors resistant to these conditions. This work presents a low-cost technique using image analysis and the hs v ( hue, saturation, and value ) color system to measure the pH in atmospheric and pressurized systems. First, a calibration curve was prepared with buffer solutions in a pH range from 2 to 10 using a mixture of pH indicators whose color varies at each pH unit. The hsv color system was determined at pressures up to 6.0 MPa and correlated to the pH of each buffer solution. Second, to evaluate the reliability of the relation between pH and hue, an acid-base titration curve with HCl and NaOH was performed. During the titration, the pH was monitored with a pH meter and the results were in good agreement with those obtained from the pH-hue correlation. Finally, to corroborate the applicability of the method in a pressurized system, the CO 2 -H 2 O system was studied, determining the pH of pure water pressurized between 0.1 and 5.0 MPa with CO 2 at 298 K. The results were similar to theoretical pH values calculated from the solubility of CO 2 in water at the experimental conditions. Hence, we have provided a new low-cost method using real-time image analysis and the hsv color system to quantify pH values in atmospheric and pressurized systems, in which the detection sensing achieves accurate measurements