Combined Voltammetric Measurement of pH and Free Chlorine Speciation Using a Micro-Spot sp2 Bonded Carbon–Boron Doped Diamond Electrode

• Published in: Analytical chemistry (Washington) 2020-12, Vol.92 (24), p.16072-16078
• Main Authors: Lucio, Anthony J, Macpherson, Julie V
• Format: Article
• Language: English
• Subjects: Aeration; Analytical chemistry; Bonding; Boron; Carbon; Chemistry; Chlorine; Diamonds; Electrodes; Electron transfer; Oxidation; pH effects; Quinones; Speciation; Voltammetry
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/acs.analchem.0c03692

This work demonstrates the use of an sp2-bonded carbon microspot boron doped diamond (BDD) electrode for voltammetric measurement of both pH and analyte concentration in a pH-dependent speciation process. In particular, the electrode was employed for the voltammetric detection of pH and hypochlorite (OCl–) in unbuffered, aerated solutions over the pH range 4–10. Knowledge of both pH and [OCl–] is essential for determination of free chlorine concentration. The whole surface of the microspot BDD electrode was found active toward the voltammetric oxidation of OCl–, with OCl– showing a characteristic response at +1.5 V vs SCE. In contrast, it was only the surface integrated quinones (Q) in sp2-bonded carbon regions of the BDD electrode that were responsible for the voltammetric pH signal. A Nernstian response for pH (gradient = 63 ± 1 mV pH–1) was determined from proton coupled electron transfer at the BDD-Q electrode, over the potential range −0.4–0.5 V vs SCE. By measuring both OCl– and pH voltammetrically, over the pH range 4–10, the OCl– oxidative current was found to correlate extremely well with the predicted pH-dependent [OCl–] speciation profile.