The Advantages of Increasing Field Strength

It is well-known that increasing the field strength of an NMR spectrometer increases the signal dispersion of signals in an NMR spectrum.[1,2] An increase of magnetic field strength can be advantageous for resolving between signals with relatively close chemical shifts. Additionally, it increases the signal-to-noise ratio (SNR), which is especially beneficial for low concentrated samples and less sensitive nuclides.[3] To illustrate these advantages, we compared data acquired with the same number of scans on our 60 and 100 MHz spectrometers:

Figure 1. ¹H NMR spectra of a 250 mM solution of acetanilide in DMSO-d₆ acquired at 60 MHz and 100 MHz.

In Figure 1, we observe a significant difference between the two magnetic strengths, especially when we zoom into the aromatic region in the ¹H NMR spectra. At 60 MHz, we observe significant overlap between the three diagnostic aromatic signals, making differentiation quite difficult. Whereas at 100 MHz, we observe full baseline separation and fine structure of the doublet-like and two triplet-like peaks. This allows for easier integration of the signals centered at 7.0, 7.3, and 7.6 ppm.

Figure 2. ¹H NMR spectra of a 250 mM solution of diethyl phthalate in CDCl₃ acquired at 60 MHz and 100 MHz.

In Figure 2, we observe a similar phenomenon between the ¹H NMR spectra acquired at 60 and 100 MHz. Where the signals corresponding to the two distinct aromatic protons (centered at 7.5 and 7.7 ppm) of diethyl phthalate are clearly separated at 100 MHz, but not at 60 MHz. Hence, the increase in magnetic strength allows us to integrate the signals separately (with more confidence) as opposed to the whole region. In addition, we better observe the AA’XX’ aromatic splitting at 100 MHz.

Figure 3. ¹³C{¹H} NMR spectra of a 1000 mM solution of tadalafil in CDCl₃ acquired at 15 MHz and 25 MHz.

For more complicated molecules like tadalafil, signal overlap is more prevalent at lower field strengths relative to higher field strengths. This does not mean that the information is not there at lower field, it means that it is harder to identify through visually inspection alone. As we observe in the ¹³C{¹H} NMR spectra in Figure 3, lots of unique carbon signals that pertain to tadalafil. At 100 MHz, due to the spectrometer’s superior signal dispersion, we observe all 22 unique carbon signals. At 60 MHz, we observe lower signal dispersion which is evident when comparing the aromatic carbons (100 – 150 ppm). We also observe complete overlap between two alkyl methine carbon signals at 55 ppm at 60 MHz, whilst at 100 MHz we observe some overlap between the two signals. With the superior SNR of the 100 MHz spectrometer, data can be acquired in significantly less time relative to the data acquired at 60 MHz. This can be crucial if one is sample limited and is running longer experiments.

Taking together these examples demonstrate the advantages of increasing the field strength from a lower field to 100 MHz. Check out our paper if you are interested in seeing how the data from our instruments compares to high field. If you are keen on implementing benchtop NMR to your workflow, please send us your samples since a 60 MHz spectrometer could be a sufficient field strength for your needs. Further, if you have a lower frequency spectrometer and are looking to upgrade to 100 MHz, please don’t hesitate to reach out to us.

References

[1] Zeng, Q.; Chen, J.; Lin, Y.; Chen, Z. Boosting resolution in NMR spectroscopy by chemical shift upscaling. Analytica Chimica Acta 2020, 1110, 109–114.
DOI: 10.1016/j.aca.2020.03.032.

[2] What you should know about signal dispersion in benchtop NMR: https://www.nanalysis.com/nmready-blog/what-you-should-know-about-signal-dispersion-in-benchtop-nmr(accessed August 17, 2026)

[3] Lee J. H.; Okuno, Y.; Cavagnero, S.; Sensitivity enhancement in solution NMR: emerging ideas and new frontiers. J Magn Reson. 2014, 241, 18 –31.
DOI: 10.1016/j.jmr.2014.01.005