Why is NMR an insensitive technique?
1 Answer
Apr 1, 2015
NMR is an insensitive technique because it requires a relatively large amount of sample to make a measurement.
For example, a mass spectrometry experiment requires about 1 µg of sample, but an NMR experiment requires 5 to 25 mg of sample.
The insensitivity arises because of the small energy difference between the two spin states of a hydrogen atom.
Only about 1 in 10⁵ H atoms are in the high-energy state at a given time, so the NMR signal is very weak.
We must do everything we possibly can to increase the signal-to noise-ratio.
There are several ways to do this:
- Use a high concentration of sample.
- Run many scans and average the signal.
- Use a higher magnetic field to increase the energy difference between the states.
