Abstract
Seawater pH standard material is determined by potentiometric methods with hydrogen electrode silver / silver chloride electrode in non-liquid junction cell. As a standard material, uncertainty is an important quality parameter. The sources of the uncertainty of determination methods mainly include measurement repeatability and temperature, atmospheric pressure, electrode potential, chloride concentration and so on. According to the experimental data, the expanded uncertainty of the method is 0.004. Finally, through in-depth analysis of the influence weight of each component, it is found that the quality control of the standard electrode potential, measurement repeatability and chloride ion concentration of the electrode in the ion system is the key to ensure the accuracy of the setting value, which provides a reliable guarantee for the replication of reference materials.
Highlights
Seawater pH is an important parameter to study seawater acidification and marine carbon cycle system
The liquid junction potential difference is included in the determination of pH value of seawater samples by using existing reference materials, and the current liquid junction potential difference cannot be measured or calculated [1]
Taking salinity 35 as an example, this paper analyzes the influencing factors in the process of setting value one by one, and calculates them respectively according to the setting value data, and obtains the expanded uncertainty of the method of setting value of seawater pH reference material
Summary
Seawater pH is an important parameter to study seawater acidification and marine carbon cycle system. There is a liquid junction potential between the external reference solution of the reference electrode and the solution to be measured (existing reference materials and seawater samples). The liquid junction potential is different due to the difference between the reference materials and seawater samples. The liquid junction potential difference is included in the determination of pH value of seawater samples by using existing reference materials, and the current liquid junction potential difference cannot be measured or calculated [1]. The ionic strength of the reference material is the same as that of seawater sample, which makes the liquid junction potential offset each other. Different from existing seawater pH measurement methods, pH is determined without liquid junction, while the influence of sulphate ion in seawater and salinity is considered here. Taking salinity 35 as an example, this paper analyzes the influencing factors in the process of setting value one by one, and calculates them respectively according to the setting value data, and obtains the expanded uncertainty of the method of setting value of seawater pH reference material
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