Thin-Layer Chemical Modulations by a Combined Selective Proton Pump and pH Probe for Direct Alkalinity Detection

Current Trends of Analytical Techniques for Total Alkalinity Measurement in Water Samples: A Review

Increasing acidity of seawater caused by increasing anthropogenic carbon dioxide absorbed into the seawater attracted the interest of researchers due to increased concern on the deterioration of marine systems and food supply to humans. Total alkalinity (TA) is one of the important parameters in determining carbonate chemistry and is described as the capacity of the sample to neutralize acids. Over the last two decades, many analytical techniques have been developed to determine TA. This article presents a review of different analytical techniques including titration, colorimetric, spectrophotometric, and potentiometric analyses in measuring TA. Among these analytical techniques, potentiometry analysis, which utilizes electrode systems such as glass electrode and ion-selective electrode used as indicator electrodes, is the most used technique. Important features such as principle, limitations, and challenges of the involved technique are discussed in detail.

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 (A_T) 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 A_T. 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 A_T in under 40 s. This method of measuring A_T, 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^-, CO₃^2-, B(OH)₄^-, PO₄^3-) of seawater A_T. The seawater measurements are consistent with the design in reaching the benchmark goal of 0.5% precision in A_T over the range of seawater A_T of ∼2200-2500 μmol kg^-1 which demonstrates great potential for autonomous sensing.