A 300 MHz NMR during a nitrogen fill
First day of classes! So, here’s a quick photo from the lab for today.
This instrument, called a NMR (nuclear magnetic resonance), is the basis for a lot of my research. NMR measures the spin signals of atoms, typically hydrogen. Through application of an electro-magnetic pulse, the vibrations of nuclei can be measured and placed on a spectrum. Frequencies of vibrations vary according to factors such as the molecule’s composition and overall geometry. Thus, NMR helps us to identify the structure of a compound.
Samples, in special tubes, are inserted at the top of the instrument, with the sample cushioned by a flow of nitrogen air. When the air flow is decreased, the sample slowly comes to rest at the center of the magnet, surrounded by a coil. This coil is immersed in liquid helium to allow it to be a superconductor, and thus be charged to have high magnetic field strength. Liquid nitrogen, contained in a dewar surrounding the liquid helium, acts as a heat sink so that the liquid helium does not rapidly boil off. This doesn’t completely prevent the liquid helium from boiling off, but since liquid helium is expensive and liquid nitrogen fairly cheap, it makes sense to use liquid nitrogen to slow the loss of helium. Thus, we have to replace the liquid nitrogen, aka do a ‘nitrogen fill’, roughly once a week.