In the present work, we use Raman spectroscopy as sensitive tool for the characterization of graphene samples. We observed diverse shifts in the position of the Raman mode close to 2650 cm–1 in various as-prepared graphene flakes. In order to elucidate the reason for this variation, we checked different substrates (Si/SiO2 and Si/Al2O3) and the effect of the annealing of graphene in argon. We find that most of as-prepared graphene flakes were non-intentional doped by holes, i.e. by physisorbed water and/or oxygen.