Long‐term stability and storage of meta‐cresol purple solutions for seawater pH measurements
Long‐term stability and storage of meta‐cresol purple solutions for seawater pH measurements
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用于海水 pH 测量的间甲酚紫溶液的长期稳定性和储存
DOI：
10.1002/lom3.10462
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Woosley, Ryan J.
中科院分区：
文献类型：
--
作者：
Woosley, Ryan J.
人为影响造成的海水pH值变化，称为海洋酸化，具有重大影响。监测和评估海洋酸化需要许多实验室几十年来进行的高度精确的测量。分光光度法可以实现短期重复性，但研究之间的可比性不太确定。所使用的指标对测量质量起着重要作用。已知用于大多数海水pH测量的Meta-甲酚紫（mCp）在暴露于紫外光下时会分解，这可能影响指示剂的长期稳定性，从而影响测量质量。在此，使用经认证的参比物质和2-羟甲基-1，3-丙二醇（TRIS）缓冲液评估mCp溶液的长期稳定性。发现纯化的指示剂溶液在室温下避光容器中可稳定（在0.0025范围内）至少5.3年。未纯化的指示剂中的不稳定性使得稳定性评估不确定。这种长期稳定性最大限度地减少了比较测量结果时的一个潜在不确定性来源，并且可以通过不过早处置仍然可用的指示剂溶液来降低成本和浪费。指示剂溶液pH值的变化表明应定期确定指示剂扰动校正。用于测定杂质的A434校正方法可用作质量保证措施，通过在指示剂溶液的寿命期间进行测量，以监测溶液中的变化。然而，计算所需的摩尔吸光系数的选择会影响校正的幅度，因此需要进一步研究，以改进对不纯指标进行校正的最佳做法。
Changes in seawater pH resulting from anthropogenic influence, termed ocean acidification, have significant implications. Monitoring and evaluating ocean acidification requires highly precise measurements comparable among many laboratories over decades. Short‐term repeatability can be achieved with spectrophotometric methods, but comparability among studies is much less certain. The indicator used plays an important role in measurement quality. Meta‐cresol purple (mCp), which is used for most seawater pH measurements, is known to break down under exposure to ultraviolet light, which can impact the long‐term stability of the indicator, and thus the quality of the measurements. Here, certified reference material and 2‐hydroxymethyl‐1,3‐propanediol (TRIS) buffers were used to assess the long‐term stability of mCp solutions. Purified indicator solutions were found to be stable (within 0.0025) at room temperature in a dark container for at least 5.3 years. Uncertainties in unpurified indicators made the stability assessment inconclusive. Such long‐term stability minimizes one potential source of uncertainty when comparing measurements and can reduce costs and waste by not prematurely disposing of indicator solutions that remain useable. Changes in the pH of the indicator solution indicate the indicator perturbation correction should be regularly determined. TheA434impcorrection method for determining impurities could be used as a quality assurance measure by making measurements over the life of the indicator solution to monitor for changes in the solution. However, the choice of molar absorptivities required for the calculation impacts the magnitude of the correction and thus warrants further study to improve best practices for making corrections to impure indicators.
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