Project Details:

pH Measurement in Seawater

Natural seawaters are polyelectrolyte solutions of high ionic strength where ion concentrations of the dissolved substances strongly influence the pH values.

The pH measurement and the study of proton transfer reactions in seawater are some of the metrological critical areas of marine chemistry, in need of establishing traceability of measured pH to the SI, with reduced uncertainty, essential for comparability of the measurements results and their interpretation. This demands generally accepted procedures including calibration standards for pH measurements to examine the proton effect on processes in the oceans.

The complexity of the pH concept leads to problems both with the comparability of the measurements results and with their interpretation. This situation becomes critical, especially when the seawater pH decreases by 0.002-0.003 pH / year due to climate changes. Internationally accepted references for the measurement results have not been established so far.

As compulsory prerequisite to achieve measurement results with associated uncertainties lower than the observed variations in pH generally accepted methods including calibration standards for the measurements of the free concentration or activity of the proton need to be established.

The Project will provide reference procedures and validated measurement methodologies for the determination of seawater acidity establishing traceability to SI units. The Project aims to provide harmonized pH measurement procedures and to underpin the traceability of the pH data of seawater. The development of a primary reference measurement procedure with the potentiometric Harned cell method will lead to a characterization of artificial seawater of reference composition which will be suitable as calibration standard for pH measurements.

Target deliverables are:

• Provision of thermodynamic data of seawater calculated from the obtained measurement results.
• Data characterizing synthetic seawater buffer,
• Provision of a primary reference procedure for pH measurements in seawater.
• Provision of harmonized and validated pH measurement procedures with respect to potentiometric pH measurements in seawater.
• Provision of uncertainty budgets according to GUM, with respect to potentiometric and spectrophotometric pH measurement methods in seawater.
• A good practice guide for pH measurements in seawater.

 

• Camões, Maria

• Bastkowski, Frank
• Dickson, Andrew
• Hioki, Akiharu
• Pratt, Kenneth
• Schneider, Bernd
• Spitzer, Petra
• Stoica, Daniela