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In order to apply Laser Induced Breakdown Spectroscopy (LIBS) for diagnostics of fuel retention and removal and wall composition in ITER it is necessary to validate the method in terms of repeatability and quality of its results for mixed, especially ITER relevant materials and its sensitivity to thin layers which contain small amounts of retained fuel. The experiments, which are within the scope of this paper were carried out at the IPPLM Warsaw to assess the method for the laser treatment of ASDEX Upgrade (AUG) strike-point tiles and calibrated C:W:Al samples prepared by the Institute of Electronic Materials Technology (IEMT). The samples under investigation contained hydrogen isotopes in the ITER-relevant mixed material layer (as the Beryllium analogue, Al was used). An electrostatic ion energy analyzer was used as the auxiliary diagnostics. The results proved that optical spectroscopy, although not straightforward in use, can give reliable results even for small amounts of fuel present in the mixed-material layer, although more effort should be put into investigating calibrated samples, to optimize the method itself and to yield a quantitative measure of fuel retention.