THE USE OF BUFFERS TO MEASURE THE PH OF SEAWATER

The pH of seawater can be measured in the field using potentiometric a nd spectrophotometric methods. The use of pH standards or buffers is a n important aspect of the calibration of both methods in a laboratory on a common concentration scale. The buffers can also be used to monit or the performance of pH meter and spectrophotometer during a cruise. A procedure is described for the determination of the pH of seawater, where the proton concentration is expressed as moles kg-H2O(-1) using seawater buffers. The buffers are prepared in synthetic seawater in th e laboratory by the methods outlined by Bates and coworkers. We have p repared four buffers (Bis, Tris, Morpholine and 2-Aminopyridine) that cover a pH range from 6.8 to 8.8. The emf values of the buffers were m easured with a H-2, Pt/AgCl, Ag electrode system after their preparati on and bottling for use at sea. The measured emf values were found to be in good agreement (+/-0.05 mV) with the original measurements of Ba tes and coworkers from 0 to 45 degrees C. The measured pH of these buf fers are in good agreement (+/-0.001 pH units) with the values calcula ted from the equations of Dickson on the total pH scale based on Bates et al. Studies are underway to access the long term stability of thes e buffers. We have also used these buffers to calibrate systems used t o make potentiometric and spectrophotometric measurements of pH on sea water relative to the H-2, Pt/Ag, AgCl electrode from 5 to 45 degrees C.