The segmental motion of poly(ethylene oxide) grafted on silica has been investigated by H-1 and C-13 magnetic resonance. The local monomer units concentration on an interface is evaluated. Two independent techniques, namely magnetic relaxation and magic angle spinning, are used and give a good agreement for the physical parameters describing the monomer units concentration on the surface. This behavior has been studied as a function of molecular weight of the chains, and each time also as a function of temperature.