A high precision, fast response, and low power consumption in situ optical fiber chemical pCO2 sensor

Abstract A sensor system suitable for monitoring changes in partial pressure of carbon dioxide ( p CO 2 ) in surface seawater or in the atmosphere has been developed. Surface seawater samples are pumped into a PVC tube enclosing an inner Teflon AF tube, which served as a long pathlength gas-permeable liquid-core waveguide for spectrophotometry. The Teflon cell contains a pH-sensitive indicator-buffer solution consisting of bromothymol blue (BTB) and sodium carbonate. Carbon dioxide in the sample diffuses into the indicator-buffer solution to reach equilibrium, resulting in pH changes, which are detected by changes in the absorbance of BTB at wavelengths of 620 and 434 nm. The p CO 2 in the sample is then derived from the pH change. The sensor has a response time of 2 min at the 95% equilibrium value and a measurement precision of 0.26–0.37% in the range 200–800 μatm p CO 2 . This chemical sensor takes advantage of a combination of long pathlength, multiple wavelength detection, indicator solution renewal, and in situ automatic control technology, and has the feature of low power consumption (the average being ∼4 W with a peak of ∼8 W).