Purification and Calibration of Indicators for Measurement of Seawater pH

燃烧化石燃料所产生的不断增加的大气二氧化碳极有可能导致严重的全球变暖（IPCC, 2007）。大气中二氧化碳含量上升的一个较少被讨论的方面是海洋酸化。最近（2006年）对沿152 W的1991年北太平洋样带的重新占领显示，水柱上部200米的pH值变化约为0.025 pH单位（Byrne等，in prep）。这种变化很重要，因为pH值对溶液形态和生物利用度、表面化学（包括活细胞）、矿物溶解度（包括钙质生物）以及氧化和还原动力学有很强的影响。在0.0004 pH单位的数量级上，分光光度测量提供了一种快速和精确的监测酸化的短期和长期尺度的手段。自1990年以来，分光光度法pH测量已广泛用于海洋和河口pH分析。然而，由于杂质的存在，在不同浓度的指示染料中，pH指示剂的校准可能变得不可靠。根据指示剂的来源（制造商）的不同，杂质会导致pH值差异大至0.01个单位。因此，比较从不同实验室获得的海水pH值结果是有问题的。在这个项目中，南佛罗里达大学的研究人员将对不同pH指示剂的杂质进行表征，并对指示剂进行纯化。纯化的指标将作为标准参考材料，并将提供给研究界。纯化后的指示剂将通过实验仔细地重新表征（平衡常数和摩尔吸光度比的测量），以提供真正的免校准测量。公布最佳纯化程序将使研究人员能够纯化自己的指标。使用校准的pH参考物质也将使研究人员能够纠正以前用不纯试剂获得的数据。就更广泛的影响而言，该项目将以研究生教育为重点。南加州大学海洋科学学院在少数民族参与研究生研究和教育方面有着良好的记录。首席研究员担任两名少数民族学生的主要顾问。海洋科学学院有面向高中生和本科生的拓展项目。该计划成功地让本科生参与研究和发表论文。该计划还将促进少数民族学生、本科生和研究生的机会。

It is highly probable that the ever-increasing atmospheric CO2 from fossil fuel burning will lead to substantial global warming (IPCC, 2007). A less-discussed aspect of rising atmospheric CO2 is ocean acidification. A recent reoccupation (2006) of a 1991 North Pacific transect along 152 W revealed pH changes in the upper 200 meters of the water column on the order of 0.025 pH units (Byrne et al., in prep). Such changes are important because pH has a very strong influence on solution speciation and bioavailability, surface chemistry (including that of living cells), mineral solubility (including that of calcareous organisms), and oxidation and reduction kinetics. With on-board precision on the order of 0.0004 pH units, spectrophotometric measurements offer a quick and precise means of monitoring acidification on both short and long-term scales. Since 1990 spectrophotometric pH measurements have been widely used in oceanic and estuarine pH analysis. However due to the presence of impurities, at variable concentrations in indicator dyes, the calibrations of pH indicators can become unreliable. Depending on the source (manufacturer) of an indicator, impurities can cause pH differences as large as 0.01 units. As such, comparison of seawater pH results obtained from different labs is rendered problematic. In this project, researchers at the University of South Florida will characterize the impurities of different pH indicators and purify the indicators. The purified indicators will serve as standard reference materials and will be made available to the research community. Purified indicators will be carefully re-characterized experimentally (measurements of equilibrium constants and molar absorbance ratios) to provide truly calibration-free measurements. Publication of the optimal purification procedures will allow researchers to purify their own indicators. Use of calibrated pH reference materials will also allow researchers to correct data that had been obtained previously with impure reagents. In terms of broader impacts, this project will feature graduate student education as a key priority. The USF College of Marine Science has a strong record of innovative minority participation in graduate student research and education. The principal investigator serves as principal advisor to two minority students. The College of Marine Science has outreach programs for both high school students and undergraduates. The PI has successfully involved participating undergraduate students in both research and publication. The proposed project will also promote opportunities for minority students, undergraduate students, and graduate students.