In the first chapter of my thesis I present a brief overview of analytical methods used in food chemistry such as IR, Raman, NMR, UV/Vis, fluorescence spectroscopy, chromatography, electronic nose, DNA- based technology, thermal techniques. The second chapter is dedicated to the analysis of ascorbic acid. It describes a new method for calculating site-specific 13C relative abundances in vitamin C samples.A modern study for the territorial classification of wines is presented in the third chapter. The fourth chapter examines a couple of synthetic procedures for the preparation of a long chain alcohol (octacosanol) and the use of IRMS to discriminate samples coming from different synthetic or natural pathways. The last chapter is a description of the work done during the visiting period in the Department of Geological Science in Bloomington (Indiana, U.S.).