CALIBRATING TRIS BUFFERS FOR PH MEASUREMENTS IN NATURAL SEAWATER

Accurate and precise measurements of seawater pH are important to understand the changes experienced in seawater as a result of the uptake of anthropogenic carbon; this translates into an increase in dissolved carbon dioxide. Seawater pH can be determined using either potentiometric or spectrophotometric techniques. TRIS buffers are used to calibrate the pH measurements; however, TRIS buffers have only been calibrated in artificial seawater. Here we present pH measurements using the Total Hydrogen Scale (pH_T) and the Seawater Scale (pH_sws) in natural seawater. Using a spectrophotometer to measure pH of TRIS buffers in real seawater, we aim to derive an equation that can accurately calibrate pH values of natural seawater over temperature and salinity ranges of 15 to 40° Celsius and 5 to 35, respectively. Past literature has successfully calibrated the instruments using TRIS in artificial waters; this research presents the first formula for calibrating pH measurements using natural seawaters. By using natural seawater, a more accurate measurement of pH can be calculated for water ranging from estuaries to open ocean seawater.