For the functionalisation of electrode surfaces by organic molecules, platinum substrates offer the advantage of forming stable adsorption bonds to the molecules. The chemical stability and surface coverage of several adsorbed crown ethers, 18-crown-6 (18C6), benzo-18-crown-6 (B18C6) and 4'-amino-dibenzo-18-crown-6 (4'-ADB18C6) and for competitive purposes methoxy-benzene, have been studied at single- and polycrystalline platinum surfaces in 0.5 M sulphuric acid with differential electrochemical mass spectrometry (DEMS). The crown ethers adsorb chemically intact in a limited potential region between 200 and 800 mV vs. RHE. They undergo reductive cleaving of the ether:ring moieties during cathodic potential shifts down to - 100 mV. By (CO)-C-13 co-adsorption and subsequent oxidative desorption, the stability and reversibility of the adsorption of the crown ethers was investigated. STM images of 4'-ADB18C6 reveal a disordered adsorbate layer. (c) 2005 Elsevier B.V. All rights reserved.