Department Surface Waters - Research and Management

Alkalinity titration in sediment porewater


While the determination of major ions and nutrients in small volumes of sediment porewater can be accomplished with capillary electrophoresis, alkalinity cannot be analyzed due to the large sample volume required to perform acid-base titration. Yet, alkalinity is an important indicator for key redox processes occurring in the sediment during early diagenesis.
We are developing a coulometric micro-titrator that requires 50 µl volume for a titration. The instrument runs from a laptops’ BNC connection and is based on an Arduino micro-controller platform.

Publication

A portable low cost coulometric micro-titrator for the determination of alkalinity in lake and sediment porewaters

Alkalinity is an important parameter in oceans, lakes, groundwaters and sediment porewaters as a link to the global carbon cycle. It is determined by classic titration with acid where sufficient sample volume is available. However, application to the limited amounts of sediment porewater requires a different approach. A portable low cost coulometric micro-titrator based on a RuO2 pH-sensitive electrode and a Ag/AgCl reference electrode requiring 50 μl of total sample volume is presented. By using a distinct sandwich cell design, a well-defined titration volume could be achieved. The micro-titrator performed well within the targeted range of 1–10 mmol L−1 and a reproducibility within 3.5%. It was successfully applied to lake water and sediment porewater alkalinity measurements of Lake Lucerne and bears the potential for automation and in-situ applications.
Steinsberger, T.; Kathriner, P.; Meier, P.; Mistretta, A.; Hauser, P. C.; Müller, B. (2018) A portable low cost coulometric micro-titrator for the determination of alkalinity in lake and sediment porewaters, Sensors and Actuators B: Chemical, 255, 3558-3563, doi:10.1016/j.snb.2017.09.191, Institutional Repository