Graphene oxide (GO) is a layered structure similar to graphite, whose planes of carbon atoms are decorated by oxygen-containing groups. These groups bring hydrophilicity and reactivity to GO, as they are present on its basal plane or at the edges. Thus, their identification is essential to determine the chemical properties of GO. Amongst the possible analytical techniques, infrared spectroscopy is suitable to identify these groups. In this work, an advanced spectroscopic method, polarized attenuated total reflectance infrared spectroscopy, was used to obtain a more in-depth analysis of these reactive groups. This new approach has allowed to refine the description of the functional groups at the surface and could be used to follow the evolution surface processes in material chemistry (e.g. grafting reactions).