A vitamin-based voltammetric pH sensor that functions in buffered and unbuffered media

摘要

The determination of pH using the conventional potentiometric glass electrode is widely practised in various fields ranging from academic to industrial environments. Recent research has focused on using various redox active organic and inorganic compounds as a basis of developing novel and miniaturized voltammetric pH sensors. This report describes the electrochemistry of such a sensor that is aimed to be disposable and based on a glassy carbon (GC) electrode drop cast with redox active vitamins. Voltammetric studies in deoxygenated buffered media revealed riboflavin (VB2) and a vitamin E derivative (VEa) to be suitable as pH-dependent and independent electroactive compounds, respectively. Solid-state square-wave voltammograms of VB2 and VEa that were concurrently drop cast on a GC electrode in various pH deoxygenated and oxygenated buffered media yielded Nernstian responses of -54.3 and -53.4 mV/Delta pH respectively, with the linear plot of the potential difference of VB2 against VEa as a function of pH. Poor Nernstian responses were obtained in deoxygenated and oxygenated non-buffered media when the pH was above approximately 4. However, with the addition of a very low concentration of an acidic buffer into the reference solution, Nernstian responses of -50.0 and -50.9 mV/Delta pH were successfully achieved in deoxygenated and oxygenated weakly-buffered media, respectively. Furthermore, a strong correlation of voltammetric versus potentiometric pH highlights the suitability of the redox active vitamin compounds as a basis for a miniaturized voltammetric pH sensor.