NMR Spin-Echo
Nuclear Magnetic Resonance Spin-Echo · Also known as: CPMG pulse sequence, spin-echo NMR
The spin-echo is a fundamental nuclear magnetic resonance (NMR) pulse sequence technique introduced by Erwin Hahn in 1950. It uses a 90-degree radiofrequency pulse followed by a 180-degree refocusing pulse to create an echo, effectively reversing the effects of magnetic field inhomogeneities and allowing accurate measurement of spin relaxation properties. This technique is essential in modern NMR spectroscopy for both one-dimensional and multidimensional experiments.
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When to use it
Use spin-echo sequences to measure spin-spin (T2) relaxation times accurately, to construct multidimensional NMR experiments (COSY, HMQC, HSQC), and to suppress unwanted signals from paramagnetic impurities or solvent. The technique is preferred over simple FID when instrumental field inhomogeneity significantly broadens resonances. It assumes reasonably stable sample conditions and accessible relaxation times within experimental timescales.
Strengths & limitations
- Effectively eliminates artifacts from magnetic field inhomogeneity, improving spectral resolution
- Enables direct measurement of T2 relaxation times and characterization of spin dynamics
- Forms the basis for sophisticated multidimensional NMR pulse sequences
- Robust against many experimental imperfections when properly calibrated
- Requires precise radiofrequency pulse calibration; phase and amplitude errors degrade the refocusing efficiency
- T1 relaxation still causes signal decay and limits sensitivity
- The refocusing pulse itself can introduce artifacts if not perfectly aligned
- Not suitable for studying very rapid molecular dynamics faster than the echo time
Frequently asked
How does the spin-echo sequence differ from a simple free induction decay (FID) experiment?
An FID directly measures the signal after a 90-degree pulse and inherently includes signal loss from magnetic field inhomogeneity. The spin-echo refocuses this inhomogeneity-induced dephasing with a 180-degree pulse, so the echo signal reflects true spin-spin (T2) relaxation without the artificial broadening, yielding higher spectral resolution.
What happens if the 180-degree pulse is not perfectly calibrated?
An imperfect 180-degree pulse (e.g., 175 or 185 degrees) will only partially rephase the spins, reducing echo amplitude and introducing phase errors. This degrades both spectral resolution and the accuracy of T2 measurements. Careful pulse calibration using nutation experiments is essential.
Can spin-echo sequences be used for three-dimensional NMR experiments?
Yes. Spin-echo building blocks are combined with additional encoding pulses and delays to create multidimensional experiments like 3D HSQC-TOCSY. The echo refocusing is maintained while additional evolution periods encode information in orthogonal frequency dimensions.
Sources
- Hahn, E. L. (1950). Spin echoes. Physical Review, 80(4), 580-594. DOI: 10.1103/PhysRev.80.580 ↗
- Carr, H. Y., & Purcell, E. M. (1954). Effects of diffusion on free precession in nuclear magnetic resonance experiments. Physical Review, 94(3), 630-638. DOI: 10.1103/PhysRev.94.630 ↗
- Meiboom, S., & Gill, D. (1958). Modified spin-echo method for measuring nuclear relaxation times. Review of Scientific Instruments, 29(10), 688-691. DOI: 10.1063/1.1716296 ↗
How to cite this page
ScholarGate. (2026, June 3). Nuclear Magnetic Resonance Spin-Echo. ScholarGate. https://scholargate.app/en/spectroscopy/nmr-spin-echo
Which method?
Set this method beside its closest kin and read them side by side — the library lays the books on the table; the choice is yours.
- COSYSpectroscopy↔ compare
- FT-ICR Mass SpectrometrySpectroscopy↔ compare
- HSQCSpectroscopy↔ compare
- NOESYSpectroscopy↔ compare