The adsorption of citrate on Au(111) from citric acid containing electrolytes has been quantified using in situ subtractively normalised interfacial Fourier transform infrared spectroscopy (SNIFTIRS). These spectra, together with spectral simulations, provide evidence that citric acid, which contains 3 carboxylic acid groups, deprotonates fully upon adsorption. Spectral simulations are consistent with a limiting coverage of about 3 x 10(-10) mol cm(-2) and the surface bound carboxylate groups adopting a tilted orientation. A model for the molecular adsorption is proposed. (C) 2003 Elsevier B.V. All rights reserved.