Feb 17, 2025
Hahn Echo for High-Gamma Nuclei
This protocol is a draft, published without a DOI.
- Alexander L. Paterson1
- 1National Magnetic Resonance Facility at Madison (NMRFAM), University of Wisconsin-Madison, Madison, WI, United States
Protocol Citation: Alexander L. Paterson 2025. Hahn Echo for High-Gamma Nuclei. protocols.io https://protocols.io/view/hahn-echo-for-high-gamma-nuclei-dd7j29kn
License: This is an open access protocol distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Protocol status: In development
We are still developing and optimizing this protocol, but it should be functional. We hope to solicit feedback primarily on clarity and usability. We intend to publish it in June 2025.
Created: May 22, 2024
Last Modified: February 17, 2025
Protocol Integer ID: 100299
Keywords: Materials High-Gamma Spin-1/2 Spin Echo
Funders Acknowledgements:
National Science Foundation
Grant ID: 1946970
Abstract
Purpose
To acquire a spin echo spectrum of highly sensitive high-gamma (i.e., 1H, 19F) spin-1/2 nucleus with half-echo acquisition.
Scope
This SOP is used to acquire a one-dimensional spin echo spectrum with half-echo acquisition, using a 90°-180° pulse pair. It is effective at suppressing background signals from rotor or stator components, and at mitigating long ringdown periods. When conducted under MAS, it should be rotor synchronized. Proper synchronization requires adjustment of the pre-acquisition delay to account for timing delays which may differ from instrument to instrument.
Guidelines
This sequence imposes a T2’ weighting factor on the intensities of the resonances; while typically negligible for short echo periods, this should be considered when using long echo periods.
Both 1H and 19F spectra frequently suffer from significant background signals, both from the probe and sometimes from within the rotor itself (e.g., caps and seals). Echoes are very effective for reducing background signals from outside the coil, but much less effective for signals originating inside the coil.
Materials
Definitions:
- MAS: Magic angle spinning
- νrf: rf power
- T1: Longitudinal relaxation time constant
- T2’: Homogeneous transverse relaxation time constant
Appendix:
Figure 1. 13C Hahn echo with correctly set value of d7 and mis-set value of d7. While both spectra are correctly phased, the mis-set value leads to a baseline roll, complicating integrations.
Before start
User should be familiar with the power limitations and duty cycle of the probe being used.
Expected amount of time SOP will use: 30 minutes
Procedure
Procedure
Load the hahnecho_shortcycle.nmrfam pulse program.
Set the 90° pulse length, p1, and the 90° pulse power, plw1, to previously optimized values.
Set the length of the echo pulse by setting cnst2 to either 2 (for a 180° Hahn echo) or 1 (for a 90° solid echo).
Set the recycle delay, d1, to 1.3 × T1 if optimizing for sensitivity, or 5 × T1 if quantitative intensities are desired.
Note
Recall that the intensities are modulated by the T2’ weighting factor.
Set the spinning rate constant, cnst31, to the MAS rate in Hz.
If the sample is static, set cnst31 to 1e6.
Set the rotor period loop counter, l1, to an initial value of 1.
If the sample is static, set l1 to the desired echo delay in microseconds.
Set the pre-acquisition delay, d7, to the initial value calculated by del7.
Set the acquisition time aq to a sufficiently long value such that the FID is not truncated.
Set the number of scans, ns, to an initial value of 3.
Acquire an initial spectrum. If any background signal is sufficiently suppressed, proceed to the next step. Otherwise, increase l1 and repeat this step.
Note
As l1 is increased, the accuracy of the relative intensities will be reduced due to the T2’ weighting factor.
Observe the baseline of the spectrum. If a significant first-order phase correction (> |60°|) is required, adjust d7 until the required phase correction is minimized.
Note
del7 will typically overestimate d7 by a few microseconds. Only small adjustments (1 µs – 10 µs) should be necessary to obtain an optimal value.
Increase the number of scans, ns, to a value which will provide adequate signal-to-noise while respecting the phase cycle (3×n).
Acquire the optimized spectrum.
Protocol references
Y. Nishiyama and N. T. Duong, “Practical guides for 1H detected solid-state NMR under fast MAS for small molecules,” Journal of Magnetic Resonance Open, vol. 10-11, p. 100062, Jun. 2022. DOI: 10.1016 j.jmro.2022.100062
Protocol
NAME
Saturation Recovery with Half-Echo Acquisition
CREATED BY
NMRFAM Facility