Generally, buffers are used in electrochemistry to prevent localized pH changes at the electrode surface during electroanalysis. In the absence of buffer, pH changes can be controlled locally at the electrode surface by driving either the cathodic oxygen reduction reaction/hydrogen evolution reaction or the anodic water oxidation reaction. Under anodic conditions, hydroxide is consumed, decreasing the local pH at the electrode surface. Under cathodic conditions, hydronium is consumed, increasing the local pH at the electrode surface. Here, we take advantage of this phenomenon to electrochemically separate illicit substances <i>via </i>polarization, capitalizing on different proton-coupled electron transfer mechanisms. As a proof-of-concept, we demonstrate the ability to separate the voltametric waves of fentanyl and heroin, which oxidize at similar potentials in the absence of pH gradients. Our results indicate that polarization-induced pH gradient relaxation is a practical method for localized formal potential separations at electrified interfaces.

Voltammetric separation of heroin and fentanyl by polarization-induced pH gradient relaxation

ACS Spring 2022

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