Electrochemical Sensor for Dissolved Carbon Dioxide Measurement

Abstract

In this paper, the fabrication and evaluation of a Severinghaus-type CO 2 sensor, based on an iridium oxide (IrO x ) pH electrode, are described. An iridium oxide pH electrode and an Ag/AgCl reference electrode were housed inside a gas-permeable silicone rubber tubing in which a bicarbonate-based electrolyte solution was sealed. The internal IrO x pH electrode was produced by a new method, i.e., the pH-sensitive IrO x film was coated on the surface of an Ir metal wire by oxidation of the Ir wire in a carbonate melt at high temperature. The Ag/AgCl reference electrode was prepared by chloridizing an Ag wire in a FeCl 3 solution. The CO 2 sensor made this way showed Nernstian response to dissolved CO 2 in the range 10 Ϫ4 to 10 Ϫ2 M. Superior analytical accuracy and stability were observed for the sensor.The concentration of CO 2 in a solution is an important parameter in many biological, biochemical, and industrial processes. Therefore, a sensing technique for dissolved CO 2 is highly desirable. The Severinghaus-type CO 2 sensor is currently the most widely used device for this purpose. This type of sensor consists of a glass pH electrode, a gas-permeable membrane, and a bicarbonate-based internal electrolyte solution. 1,2 The working principle of the CO 2 sensor is based on the measurement of the pH change of the electrolyte solution caused by the hydrolysis of CO 2 . The CO 2 molecules dissolved in the test solution diffuse through the gas-permeable membrane and enter the internal solution, where they react with water to form carbonic acid, which subsequently dissociates into bicarbonate and hydrogen ions ͑see Eq. 1͒. Consequently, the produced hydrogen ions decrease the pH of the electrolyte, which is detected by the internal pH electrodeSince the first Severinghaus-type CO 2 sensor was reported in 1958, 1 many efforts have been made to improve the performance of the sensor including stability, response time, and lifetime. 3-9 However, drift reported in the literature, ranging up to 20 mV/h, remains a serious problem for practical applications of the sensor. Any drift of the internal pH electrode may cause measurement errors. The improvement of the pH electrode is the key to the development of a reliable CO 2 sensor. So far the glass electrode and Sb-SbO x electrode have been mostly used as the internal pH electrodes.Glass electrodes exhibit good sensitivity, stability, and lifetime. However, they are difficult to miniaturize, based on current manufacturing technologies, and cannot be used in food or in vivo applications because of their brittle nature and the risk of leaving sharp bits of glass behind. Furthermore, glass electrodes are expensive and unsuitable for disposable products. The Sb-SbO x electrode suffers from interference by oxygen and shows response drift. We have developed a stable IrO x pH electrode 10,11 and have constructed a Severinghaus-type CO 2 sensor by employing this IrO x electrode as the pH-sensing element. 12 In the present work, we have further improved the CO 2 sensor performance by o...

Effects of Thermal Oxidation Cycle Numbers and Hydration on IrOxpH Sensor

“…This result is better than many reported data in the literature showing the linear range of 2-12. 6,15,22,23 Although the absolute value of potentials varies with the electrodes to some extent, the pH sensitivity is quite similar (−55∼−57 mV/pH), which is close to the Nernst response. Response rate.-The potential-time curves in different pH buffer solutions were detected to evaluate pH response rate of the electrodes.…”

“…[12][13][14][15][21][22][23] Few reports involve the mechanism of pH response. Comparing with the simple ion exchange mechanism for glass pH electrode, the H + (pH) response mechanism for metal/metal oxide pH electrode is more complicated.…”

Carbon dioxide and oxygen gas sensors-possible application for monitoring quality, freshness, and safety of agricultural and food products with emphasis on importance of analytical signals and their transformation

“…Previous studies have introduced several carbon dioxide sensors, as listed in Table 1. Carbon dioxide sensors are categorized mainly into two types, optical sensors and electrochemical sensors, on the basis of their immanent chemical or physical properties (Cammaroto et al, 1998;Yao and Wang, 2002;Puligundla et al, 2012). Potential application of carbon dioxide sensors in intelligent agriculture and food packaging industry has been discussed in the earlier reviews (Neethirajan et al, 2009).…”

A downhole CO2 sensor to monitor CO2 movement in situ for geologic carbon storage

“…A number of studies have proposed various types of CO 2 sensors. [14][15][16][17] John and Joseph [15] disclosed a planar bicarbonate sensor that, combined with a pH sensor, could measure the concentration of CO 2 in water. However, the high pressures prevalent underground prevented the sensor from working correctly under such conditions.…”