Consistency and stability of purified meta-cresol purple for spectrophotometric pH measurements in seawater
Consistency and stability of purified meta-cresol purple for spectrophotometric pH measurements in seawater
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用于分光光度法测量海水 pH 值的纯化间甲酚紫的一致性和稳定性
DOI：
10.1016/j.marchem.2021.104018
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发表时间：
2021
期刊：
影响因子：
3
通讯作者：
Watanabe, Shu-ichi
中科院分区：
文献类型：
--
作者：
Takeshita, Yuichiro;Warren, Joseph K.;Liu, Xuewu;Spaulding, Reggie S.;Byrne, Robert H.;Carter, Brendan R.;DeGrandpre, Michael D.;Murata, Akihiko;Watanabe, Shu-ichi
对全球水文数据产品的分析表明，使用纯化的间甲酚紫（mCP）测量的总规模pH值（pHspec）与根据总碱度和溶解无机碳计算的pH值之间存在明显的pH值依赖性差异。然而，这主要是基于美国的巡航，最近的三次日本巡航没有显示这种pH依赖性差异。一种可能的解释是，从不同机构获得的纯化mCP批次导致pH值显著不同。在这里，我们通过比较从四个不同机构获得的纯化的mCP的性能来测试这一假设。我们证明pH值始终为±0.0012（95% CI）当适当地去除杂质时，可以实现与机构无关的目的。然而，四个机构中至少有三个机构的一个批次具有显著的pH依赖性误差，高达-0.008。使用HPLC和分光光度法（对于9例中的8例，尽管后者仍存在问题）鉴别了导致pH依赖性错误的杂质的存在。我们的结论是，由于纯化过程后残留的杂质导致的pH值依赖性误差本身太小，无法解释最近一组巡航之间观察到的差异。确定这种差异的来源应该是一个首要任务。这项研究还强调了建立强大的质量保证和质量控制协议的重要性，以确保与以前公布的方程计算pH值的行为一致。我们建议一个集中的系统，其中一个或几个机构分配纯化的mCP为社区，因为这种分配方法将导致更低的价格和简化质量保证。
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.
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