Abstract
Seawater pH is a valuable parameter to describe ocean acidification. However, pH measurements are often subject to large uncertainty and the results of the pH comparison from different laboratories are not convincing. We assessed the potentiometric method for pH measurement on seawater samples with salinities from 20 to 40 and pH ranging from 7.2 to 8.6. pH glass electrodes were calibrated using both commercially available NBS buffers and the equimolal Tris (2‐amino‐2‐hydroxymethyl‐1,3‐propanediol) buffer (prepared in synthetic seawater at a salinity of 35). The results demonstrated that the uncertainty in pH measurements was within ± 0.01 in the entire salinity range and was better than ± 0.003, when the sample salinity was close to that of equimolal Tris buffer (salinity difference within ± 2.5), regardless of the sample pH. This study suggests that if the electrode calibration is performed properly, the potentiometric method can fulfill the “weather” goal (± 0.02) of the Global Ocean Acidification Observing Network in pH measurements; it might even meet the “climate” goal (± 0.003) if the difference between the salinity of the samples and the Tris buffer is small.
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Acknowledgements
This work was financially supported by the Guangdong Basic and Applied Basic Research Foundation (2021B1515120080), the National Key Research and Development Program of China (2020YFA0608304), the Key Research and Development Program of Shandong Province (2020ZLYS04) and the Young Scholars Program of Shandong University (2018WLJH43). We are grateful to Prof. Andrew Dickson and two anonymous reviewers for their thoughtful comments and suggestions.
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Hu, YB., Chen, LC. & Mou, L. Quality control of potentiometric pH measurements with a combination of NBS and Tris buffers at salinities from 20 to 40 and pH from 7.2 to 8.6. J Oceanogr 78, 467–473 (2022). https://doi.org/10.1007/s10872-022-00654-5
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DOI: https://doi.org/10.1007/s10872-022-00654-5