Chemical analysis of structures in the nanometre range is a challenge even with modern analytical transmission electron microscopes (TEM). In this work we demonstrate that it is possible to measure chemical variations in the monolayer scale and identify compounds formed at the interfaces by using Valence Electron Energy Loss Spectroscopy (VEELS) in STEM line-scan mode. We discuss the impact of valence electrons delocalisation on the spatial resolution of our experiments. The method is tested first on a model sample containing a 4 nm HfO(2) layer. The limitations of VEELS to provide chemical analysis are then explored and discussed by applying this technique to a real semiconductor device containing a 2 nm HfO(2) layer.