We present a novel combination of in situ attenuated total reflection-infrared spectroscopy (ATR-FTIRS) and on-line differential electrochemical mass spectrometry (DEMS) via a dual thin-layer electrochemical flow-cell, which allows: (i) simultaneous detection of stable adsorbed species and adsorbed reactive intermediates and side products by ATR-FTIR spectroscopy, (ii) quantitative determination of volatile reaction products and by-products by DEMS, and (iii) determination of the overall reaction kinetics by measuring the Faradaic current under controlled mass transport of reactants and reaction products to and from the electrode. The wealth of information and the insight into reaction mechanism and kinetics accessible from these complementing techniques are demonstrated taking the oxidation of CO on a Pt thin film electrode as example, including the electrooxidation of a pre-adsorbed CO monolayer at constant potential (0.6 V), the open-circuit reduction of pre-formed PtO by chemical reaction with CO, and potentiodynamic continuous CO bulk electrooxidation. (c) 2007 Elsevier Ltd. All rights reserved.