Question

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

Answer 1

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.