Comparison of the relative changes to 71 Ga NMR parameters induced by each of the probe molecules highlights that the adsorption of a probe molecule to a surface Ga site mostly results in a drop in CQ with a marginal change of δiso; the significant differences in CQ between GaLA and GaBA interacting with py make it possible to distinguish these two sites by Ga NMR. Refining 71 Ga NMR data and assignment of surface structures