The chemical composition of an interface can be determined using neutron reflection by measuring the reflected signal as a function of the incident neutron wave vector. The intensity of the reflected signal is a function of the neutron scattering length density of the material in the interface region which is in turn dependent on its chemical/isotopic composition. Neutrons have the ability to penetrate many centimetres of most condensed matter without significant signal attenuation. Hence the technique of neutron reflection spectroscopy can be used to analyze buried interfaces without complex specimen preparation and can, uniquely, be used to characterise interfaces between liquids and solids. Here we present neutron reflection results from interfaces between a sapphire (Al2O3) single crystal and tin at room temperature and above its melting point. The results show deviations from the trend expected by simple density change on melting and are interpreted as evidence for oxygen segregation during wetting.