What is the external magnetic field #(B_0)# in NMR processes?

Question

Ellie Adams · Accepted Answer

When you insert an NMR tube containing your sample into the NMR machine, you are placing it between the poles of a big magnet. The external magnetic field #B_0# is the field generated by this magnet.

The field strengths of most instruments range from 1.41 T to 11.75 T.

They are usually reported in terms of the corresponding resonance frequencies of protons.

The relationship is

#B_0 = "0.023 487 T/MHz""#

So, a 100.00 MHz instrument has #B_0 ="2.3487 T"#.

Other nuclei such as #""^13"C"# have different magnetic moments, so they resonate at different frequencies.

If you have a 2.3487 T (100 MHz) instrument, you will have to use a frequency of 25.14 MHz for #""^13"C"# nuclei.

Here are the corresponding frequencies for some other nuclei.

Ava Andrews · Answer

undefined The external magnetic field (B_0) in nuclear magnetic resonance (NMR) processes is the main magnetic field applied to the sample. It aligns the nuclear spins of the sample with its direction and influences the energy levels of the spins, which is essential for the NMR phenomenon to occur.