High resolution electrochemical monitoring of small pH changes

Abstract

Usually pH measurements are carried out using potentiometric technique. However, sensitivity of this method is low due to limitation set by Nernst equation – the moderate resolution is a significant problem in today demand for tracking small pH changes in various application areas.We propose a novel approach that allows electrochemical monitoring of pH changes with resolution reaching below 0.01 units in alkaline, acidic or close to neutral media. The proposed method uses all-solid state pH sensitive electrode with syringaldazine (Syr) modified multi-walled carbon nanotubes as the reference electrode modulating amperometric signal of Ag|AgCl electrode used as the working one. Due to high slope of the current vs. potential dependence for low-polarizable silver / silver chloride electrode relatively small changes of reference (pH-sensitive) electrode potential are transformed to pronounced changes of the recorded current. Ultimately, this results in significant increase in resolution of traced pH changes. Moreover, the current recorded is found to be linearly dependent on changes of H+ or OH− ions concentration in a broad pH range, which additionally contributes to increased resolution readout. Advantages of herein proposed approach were fully verified by monitoring minute changes of solution pH resulting from dissolution of carbon dioxide.