Mass spectrometry (MS) is a cornerstone of modern analytical chemistry, offering rapid and sensitive mass-to-charge (m/z) measurements. However, its reliance on fragmentation patterns and indirect structure inference can limit its effectiveness—particularly when analyzing isomers, chiral compounds, or complex mixtures. Even advanced MS/MS methods often fall short in resolving structural ambiguities.
“Structure annotation of almost all fragment ions investigated is incorrect…”1
Molecular Rotational Resonance (MRR) provides an orthogonal approach. Rather than inferring structure from fragments, MRR directly probes gas-phase molecular geometry via rotational transitions. The result is a high-resolution, unambiguous spectral fingerprint that uniquely identifies both molecules and conformers.2
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MRR is particularly useful when mass data alone is insufficient—such as in confirming enantiomeric excess, identifying residual solvents, or distinguishing structurally similar analytes.
While not a replacement for MS, MRR offers complementary insight—particularly where structural resolution is critical.
Key Differences:
| Feature | Mass Spectrometry (MS) | Molecular Rotational Resonance (MRR) |
|---|---|---|
| Basis of Detection | Mass-to-charge (m/z) | Rotational transitions |
| Structural Specificity | Inferred from fragmentation | Direct, based on 3D structure |
| Isomer Differentiation | Often requires separation | Resolves regio- and stereoisomers directly |
| Sample Preparation | May require LC/GC | Headspace or neat sample |
| Consumables | Columns, solvents, gases | Minimal |
References
1. van Tetering, L., Spies, S., Wildeman, Q.D.K. et al. A spectroscopic test suggests that fragment ion structure annotations in MS/MS libraries are frequently incorrect. Commun Chem 7, 30 (2024). https://doi.org/10.1038/s42004-024-01112-7
2. Justin L. Neill, Alexander V. Mikhonin, Ted Chen, Reilly E. Sonstrom, Brooks H. Pate, Rapid quantification of isomeric and dehalogenated impurities in pharmaceutical raw materials using MRR spectroscopy, Journal of Pharmaceutical and Biomedical Analysis, Volume 189, 2020, 113474, ISSN 0731-7085, https://doi.org/10.1016/j.jpba.2020.113474.