Award: OCE-1658321

Additions of strong acids to natural solutions (called titrations) provide information essential to understanding the chemistry of these solutions. Natural solutions have both inorganic and organic components, and the chemistries of various inorganic components are far better understood than the organics. The inorganic components of natural solutions have identifiable total concentrations and chemical interactions that have been carefully characterized through decades of laboratory research. The behavior of organics in natural solutions is, in contrast, much less well studied. The objectives of the research described herein were to (a) improve the titration methods that are commonly used to characterize the behavior of natural dissolved organic matter and (b) characterize the acid-uptake behavior of natural organics. The methods used to study the acid-uptake characteristics of dissolved organics were improved through the development of novel procedures to facilitate the calibration of scientific instruments (electrodes) that are used to monitor titrations. The calibration procedures developed in this work can reduce measurement uncertainties by 25% or more. Our research also characterized the acid-uptake properties of dissolved organics in river water obtained on the west coast of Florida. Acid titrations were performed by comparing the acid uptake characteristics of two types of solutions. One type of solution was composed by mixing organic-rich river water with seawater collected from the Gulf of Mexico. The second type of solution was composed by mixing pure water (no organics) and Gulf of Mexico seawater in the same proportions that were used in the first titration. Comparisons of the two types of titrations revealed the existence of two categories of organics. One type of organic had a high affinity for added acid but characteristics that were somewhat variable over the course of multiple titrations. The second category of organic matter had a much lower acid affinity, and the acid affinity was substantially consistent throughout repeated titrations. In addition to titrations of river-derived organic matter, titrations were also conducted using solutions that serve as certified reference materials for calibration of acid titrations on a worldwide basis. These titrations, in conjunction with numerical (synthetic) titrations of organic matter, indicated that even widely used reference materials can contain substances (for example, organics) that can influence the interpretation of titrations with strong acids. Through characterization of the behaviors of natural dissolved organics, this research project refined the interpretation of titrations of natural solutions that contain mixed inorganic and organic components. Last Modified: 05/10/2022 Submitted by: Robert H Byrne