Purification and Calibration of Indicators for Measurement of Seawater pH

点击翻译按钮获取中文摘要

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.