Bronsted-Lowry acids and bases exert important effects on the electrochemistry of hydroquinone (QH(2)) and benzoquinone (Q) in acetonitrile. However, the "effective pH" in aprotic media has been neglected in the redox process of QH(2) and Q. Our results show that neutral proline induces new voltammetric waves for QH(2) and quinone in acetonitrile, that cannot be attributed to protonation or hydrogen bonding. We observed that only one cathodic wave and one anodic wave of quinone are produced in adequately buffered acetonitrile. Moreover, several amines generated a new anodic QH(2) wave, whereas acetic acid produced a new cathodic wave of quinone. Proline acts as proton donor and proton acceptor during the redox of QH(2) and Q, thereby indicating that the "effective pH" occurs in dilute buffered aprotic media. We thus concluded that the new waves in acetonitrile are caused by rapid pH changes at the electrode surface and not by new species. (C) 2015 The Electrochemical Society. All rights reserved.