Despite abundant research on nanoconfined liquids, determining the density, which is a key property of the liquid, remains an open problem. All the previously explored strategies indeed provide a measurement of an effective density instead of the true, intrinsic density.We therefore aim at establishing a new reliable method to measure the density of a nanoconfined liquid. We propose here to take advantage of the quantitative predictability of neutron scattering, in complement to Optical Kerr Effect spectroscopy (OKE) and molecular simulation (MD), for characterizing an archetypical hydrogen bonded liquid, acetonitrile. We expect a signature of the surface versus bulk contribution in the vibrational density of states and a direct evaluation of density fluctuations by measuring the translational and rotational motions by QENS. We require for this experiment 3 days of beam time on LET.