The invention provides for a magnetic field probe (100, 2202) comprising a container (104, 702, 1400, 1500, 1600, 1700, 1800) with a hollow cavity (106, 602). The hollow cavity comprises a duct (110, 700) connecting the hollow cavity with an exterior surface (109, 702) of the container. The container further comprises metallization (108, 800) surrounding the duct on the exterior surface. The container further comprises a metallic plug (400, 1000). The metallic plug at least partially fills the duct. The metallic plug forms a seal (402, 1002) with the metallization. The magnetic field probe further comprises a sample (300, 900, 1608) comprising fluorine 19. The sample at least partially fills the hollow cavity. The magnetic field probe further comprises an antenna (102) adjacent to the container for manipulating the magnetic spins of the fluid sample and for receiving magnetic resonance signals from the fluid sample.