In this paper, we present an integrated experimental-theoretical approach to evaluate the spectroelectrochemical response of the facilitated proton transfer processes via water autoprotolysis at the liquid vertical bar liquid (L vertical bar L) interface. The aim of these studies is to confirm theoretically and experimentally the pH gradients generated at the L vertical bar L interface using coupled electrochemical and spectroscopic techniques. The spectroelectrochemical measurements are performed using a parallel beam configuration, where the light beam passes at grazing incidence over the L vertical bar L interface. pH gradients generated by proton transfer assisted by Quinidine via water autoprotolysis are evaluated by the direct measurement of the optical absorption of Thymol Blue, acting as a pH probe. Results obtained are correlated with a numerical model considering all equilibria involved at both phases. (C) 2019 Elsevier Ltd. All rights reserved.