Abstract
Analysis of a global hydrographic data product showed a clear pH-dependent discrepancy between pH on the total scale measured spectrophotometrically (pHspec) using purified meta-Cresol Purple (mCP) and pH calculated from total alkalinity and dissolved inorganic carbon. However, this was based mainly on US cruises, and three recent Japanese cruises do not show this pH-dependent discrepancy. One potential explanation is that purified mCP batches obtained from different institutions lead to significantly different pHspec. Here, we tested this hypothesis by comparing the performance of purified mCP obtained from four different institutions. We demonstrate that consistent pH of ±0.0012 (95% C.I.) can be achieved regardless of the institution when impurities are properly removed. However, there was at least one batch from three of the four institutions that had significant pH-dependent errors that were as large as −0.008. The presence of impurities that led to pH-dependent errors was identified using HPLC and, for 8 out of the 9 cases, by spectrophotometry (although issues still remain for the latter). We conclude that pH-dependent errors due to impurities that remain after the purification process are, by themselves, too small to account for the differences observed between the recent set of cruises. Identifying the source of this difference should be a top priority. This study also highlights the importance of establishing robust quality assurance and quality control protocols to ensure consistent behavior with previously published equations to compute pH. We recommend a centralized system where one or a handful of institutions distribute purified mCP for the community, as this distribution approach will lead to lower prices and simplify quality assurance.
| Original language | English |
|---|---|
| Article number | 104018 |
| Journal | Marine Chemistry |
| Volume | 236 |
| DOIs | |
| State | Published - Nov 20 2021 |
Funding
We thank Andrew Dickson for providing the equimolar Tris buffer solutions and the pH measurements of the buffer solutions made in his laboratory. Work and personnel at MBARI was funded by the David and Lucile Packard Foundation , and NSF OCE-1736864 . MDD was supported by NSF OCE-1459255 and PLR-1504410 . JISAO/CICOES's contribution is number 2020-1122 , and PMEL's contribution is number 5202 . USF personnel acknowledge the support of NSF , project numbers OCE 1220110 and OCE 1657894 . BRC thanks the Global Ocean Monitoring and Observation division of the National Oceanic and Atmospheric Administration for funding his contributions to this effort through the Global Carbon Data Management and Synthesis Project (# 100007298 ). We are grateful to the Ocean Carbon Biogeochemistry program for funding the Ocean Carbonate System Intercomparison Forum working group, which helped foster this collaboration. We thank Andrew Dickson for providing the equimolar Tris buffer solutions and the pH measurements of the buffer solutions made in his laboratory. Work and personnel at MBARI was funded by the David and Lucile Packard Foundation, and NSF OCE-1736864. MDD was supported by NSF OCE-1459255 and PLR-1504410. JISAO/CICOES's contribution is number 2020-1122, and PMEL's contribution is number 5202. USF personnel acknowledge the support of NSF, project numbers OCE 1220110 and OCE 1657894. BRC thanks the Global Ocean Monitoring and Observation division of the National Oceanic and Atmospheric Administration for funding his contributions to this effort through the Global Carbon Data Management and Synthesis Project (#100007298). We are grateful to the Ocean Carbon Biogeochemistry program for funding the Ocean Carbonate System Intercomparison Forum working group, which helped foster this collaboration.
| Funders | Funder number |
|---|---|
| 5202 | |
| PLR-1504410, OCE 1657894, 2020-1122, OCE-1736864, OCE-1459255, OCE 1220110 | |
| David and Lucile Packard Foundation | |
| National Oceanic and Atmospheric Administration | 100007298 |
Keywords
- Meta-cresol purple
- pH