Single-Sided NMR unfortunately can't work on metal cans or other metallic containers. NMR relies on a radio frequency (RF) pulse to penetrate into the sample through a container. Aluminum will both reflect and absorb this RF when entering and exiting the sample. A single layer of standard aluminum foil would block 90-99% of the RF power reaching the sample and decrease the signal coming out an additional 90-99%. Plastics and glass don't absorb or reflect radio waves nearly as much and will always outperform metallic containers in terms of sensitivity.