pH reflects the acid-base state of water and is one of the most important parameters for quantitative description of marine chemical characteristics. Real-time tracking of changes in the pH of ocean sites can assess the impact of enhanced ocean acidification on ecosystems in the future, and it can also reflect changes in atmospheric CO2 concentrations and further understand the global carbon cycle. High-precision pH sensor is an in-situ sensor based on photometry.

Based on photometry. The indicator and seawater are pumped into the pipeline and mixed, and detected by the absorbance at the characteristic wavelength. The cresol purple was selected for the H+ reagent and the light intensity was determined based on colorimetry at three wavelengths, with the first-two absorptions as a known function of pH and the third absorption as a baseline correction. The measuring device includes waterway components, optical system, circuit control, and computer application processing software. It has high accuracy and good accuracy, which eliminates the need for baseline correction of the electrode detection method and meets the high standards of scientific researchers. Compared with the shortcomings of the electrode detection method, such as low accuracy and point drift, the photometric method, as a high-precision and stable performance method, has gradually become the standard method for measuring the pH of seawater.