Pure powders of TiC$_x$O($_{1-x}$) solid solution were synthesized through the carbothermal route. The chemical analysis of the light elements in the as-obtained TiC$_x$O($_{1-x}$) oxycarbides powders were performed by Instrumented Gas Analysis (IGA). The cell parameters of the samples were determined with an accuracy of about 2% by means of X-ray powder diffraction and the internal standard method. As a result, a model correlating the cell parameters to the chemical composition was established. These reference TiC$_x$O($_{1-x}$) oxycarbides powders were then sintered in order to obtain pellets of dense ceramics. After having determined that the sintering process does not change the chemical composition of the starting powder, chemical analysis of the different samples of the solid solution were successfully undertaken by Ion Beam Analysis techniques (IBA). The Nuclear Reaction Analysis (NRA) method - that was used to analyse light elements with very high sensitivity - was coupled with Rutherford Back Scattering (RBS) analysis in order to accurately determine the metallic over light elements ratio and to determine the stoichiometry of the phase on massive samples. Exhaustive simulations of the NRA spectra were performed and demonstrated that discrete compositions of the TiC$_x$O($_{1-x}$) can be efficiently measured locally for bulk samples. Compared to IGA results, the relative amounts of carbon and oxygen of bulk materials were determined with a bias lower than 5%. This protocol being implemented for the TiC$_x$O($_{1-x}$) system was then tested on HfC$_x$O($_{1-x}$)with the same success.