Feb 17, 2025
Version 1
Saturation Recovery with Half-Echo Acquisition V.1
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. Saturation Recovery with Half-Echo Acquisition. protocols.io https://protocols.io/view/saturation-recovery-with-half-echo-acquisition-dztu76nwVersion created by NMRFAM Facility
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: 120404
Keywords: Spin-1/2 T1 Saturation Recovery with Echo Detection
Funders Acknowledgements:
National Science Foundation
Grant ID: 1946970
Abstract
Purpose
To measure the longitudinal relaxation time, T1, of resonances present in the sample when a significant background signal is also present.
Scope
This SOP should be completed after an initial 1D experiment has been completed, but before further experiments are performed. Upon completion of this SOP, the user will be able to set recycle delays appropriate for the purpose of later experiments, either to maximize signal per unit time, or to ensure quantitative intensities.
Guidelines
If acquisition of a 1D spectrum requires substantial signal averaging, this SOP may not be appropriate.
The addition of echo detection increases the minimum number of scans required per time increment to 3. If the sensitivity of the sample is sufficient to obtain adequate signal with one scan and there is no significant background signal, instead follow the SOP for measuring T1 via saturation recovery without echo detection.
If acquisition of a 1D spectrum requires substantial signal averaging, this SOP may not be appropriate.
This SOP is intended for a beginning user who has been trained on basic spectrometer safety and principles.
This SOP is written for acquisition using a Bruker console and TopSpin 3.6.2. It may be adapted to other TopSpin versions where appropriate. The basic process is the same on TopSpin 4.x, but requires a NEO-compatible pulse sequence. The sequence satrect1_echo.neo.nmrfam is compatible.
Materials
Definitions:
- T1: Longitudinal relaxation time
- l20: Number of saturation pulse loops
- d20: Presaturation loop delay
Appendix:
If the presaturation train is not completely effective, the recovery curve might initially decrease, and then follow the expected exponential curve. This is common behaviour and can be dealt with by discarding the initial points of the curve.
The values of the variable delay list T1_standard_array range from 0.25 to 128 s, increasing by a factor of two for each increment. This should provide adequate spacing to accurately determine T1 values between 1 s and 64 s. If necessary, adjust the list for shorter or longer values of T1.
Figure 1. Example of a successful 7Li saturation recovery experiment performed on a lithium silicate glass. The T1 of this environment was found to be 3.4 s.
Safety warnings
The minimum length of d1 for the 2D experiment will depend on whether decoupling is used during acquisition. If decoupling is used, d1 should be about 20 times as long as the acquisition period, typically on the order of 1 s. If decoupling is not used, a d1 value of 100 ms may be reasonable.
Before start
User is responsible for knowing the duty cycle of the probe and instrument being used.
User is responsible for knowing the high-power decoupling limits of the probe.
Expected time to completion: 1 hour or less
Procedure
Procedure
Load the satrect1_echo.nmrfam pulse program; or, if using a NEO console, the satrect1_echo.neo.nmrfam pulse program.
Set values for the acquisition of an initial spectrum.
Set the 90° pulse length, p1, and the 90° pulse power, plw1, to previously optimized values.
- The 180° pulse, p2, is automatically calculated as 2 × p1.
Set the recycle delay, d1, to a relatively long value, e.g., 10 s.
Set the number of saturation pulse loops, l20, to 0.
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 cnst7.
If necessary, enable decoupling by setting the -Ddec flag in zgoptns.
- Set the heteronuclear decoupling program, CPDPRG2, pulse length, PCPD2, and pulse power, plw12,to the value determined by following SOP 1H Decoupling.
Set the variable delay list, vdlist, to T1_standard_array.
Acquire an initial spectrum. The number of scans should be as small as practicable to allow for adequate signal, ideally as low as 3.
Ensure that all expected resonances are visible. If some are not visible, either reduce the pulse length or increase d1, as appropriate.
If any background signal is sufficiently suppressed, proceed to the next step. Otherwise, increase l1 and repeat this step.
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.
- cnst7 will typically overestimate d7 by a few microseconds. Only small adjustments (1 µs – 10 µs) should be necessary.
Set the number of saturation pulse loops, l20, to an initial value of 20. Set the presaturation loop delay, d20, to an initial value of 1000 µs.
Acquire a spectrum. There should be no signal present.
If signal is still present, increase l20, up to a maximum of 100, and reacquire the spectrum.
If increasing l20 does not result in a null signal, reduce the number of loops and retry with longer presaturation loop delays d20.
If increasing d20 does not result in a null signal, retry with shorter presaturation loop delays d20.
Convert the experiment to a 2D experiment window. Set the following parameters:
F1 TD: 12
FnMODE: QF
F1 SI: 16
d1: A minimal value that respects the probe duty cycle, see Appendix.
Acquire the 2D experiment via the command zg.
Process the 2D experiment.
Transform the data using the command xf2.
Correct the F2 phasing of the slice with the longest delay period.
Do not transform or phase the F1 axis.
To process the data, launch the TopSpin utility t1guide and follow the workflow in the utility.
Extract the slice with the longest variable delay, i.e., the most recently acquired slice.
Integrate each resonance. Save using the option “Export Regions to Relaxation Module and .ret”.
- If resonances are not resolved, attempt to select the regions of least overlap.
- If resonances cannot be reasonably separated, integrating over all of the peaks will allow for the determination of the longest T1 component.
Enter the relaxation window and set the Fitting Function Function Type to uxnmrt1.
Calculate fit for all peaks. If successful, the fitting window should resemble the example in the appendix.
Record the T1 for each site. Use the longest value of T1 for determining the recycle delay of future experiments.
Protocol references
Bruker Solid State NMR User Manual Z4D10641B, Section 16.2.4
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.