Hexatriacontane (C36H74) has been used as a model molecule for the study of the surface modifications of high-density polyethylene (HDPE) in argon and oxygen radio-frequency (RF) plasmas. The combination of static secondary ion mass spectrometry (SIMS), ion scattering spectroscopy (ISS), X-ray photoelectron spectroscopy (XPS), and contact angle measurements has constituted a powerful method for the investigation of the surface modifications induced by the plasma treatments. The surface degradation and functionalization are shown to depend on both the nature of the treated material and the nature of the plasma atmosphere. The SSIMS results obtained on plasma-modified hexatriacontane and HDPE are compared in order to identify the nature of the functionalities present at the plasma-treated surfaces. Finally, plasma treatment 180 atmosphere was performed on HDPE, C36H74, and polystyrene (PS). In that case, the isotopic specificity of both ISS and SIMS allowed the determination of the relative concentrations of O-16 and O-18 in relation to the probed depth and plasma atmosphere.