Solid State Sensor for Simultaneous Measurement of Total Alkalinity and pH of Seawater

A novel design is demonstrated for a solid state, reagent-less sensor capable of rapid and simultaneous measurement of pH and Total Alkalinity (AT) using ion sensitive field effect transistor (ISFET) technology to provide a simplified means of characterization of the aqueous carbon dioxide system through measurement of two “master variables”: pH and AT. ISFET-based pH sensors that achieve 0.001 precision are widely used in various oceanographic applications. A modified ISFET is demonstrated to perform a nanoliter-scale acid–base titration of AT in under 40 s. This method of measuring AT, a Coulometric Diffusion Titration, involves electrolytic generation of titrant, H+, through the electrolysis of water on the surface of the chip via a microfabricated electrode eliminating the requirement of external reagents. Characterization has been performed in seawater as well as titrating individual components (i.e., OH–, HCO3–, CO32–, B(OH)4–, PO43–) of seawater AT. The seawater measurements are consistent with the...