Feb 17, 2025
Version 1
Quadrupolar Quantitative Bloch Decay V.1
- Alexander L. Paterson1
- 1National Magnetic Resonance Facility at Madison (NMRFAM), University of Wisconsin-Madison, Madison, WI, United States
Protocol Citation: Alexander L. Paterson 2025. Quadrupolar Quantitative Bloch Decay. protocols.io https://dx.doi.org/10.17504/protocols.io.n2bvjn9wngk5/v1Version 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: February 14, 2025
Last Modified: February 17, 2025
Protocol Integer ID: 120434
Keywords: Quantitative MAS Bloch Decay: 23Na, quadrupolar quantitative bloch decay purpose, 1d nmr spectra of quadrupolar nuclei, 1d bloch decay spectrum under magic angle, 1d bloch decay spectrum, quadrupolar nuclei with quantitative intensity, 1d nmr spectra, bloch decay experiment, acquisition of 1d nmr spectra, sensitivity of the bloch decay experiment, quadrupolar nuclei, nuclei, nutation on cq
Funders Acknowledgements:
National Science Foundation
Grant ID: 1946970
Abstract
Purpose
To acquire a 1D Bloch decay spectrum under magic angle spinning with quantitative intensities.
Scope
The acquisition of 1D NMR spectra of quadrupolar nuclei with quantitative intensities requires particular care due to the complex dependence of nutation on CQ. This SOP should be followed when quantitative intensities are required. If quantitative intensities are not required, the sensitivity of the Bloch decay experiment can be improved by making different choices in pulse length and d1.
Guidelines
The quantitative intensities described here are relative intensities, not absolute intensities. Determining absolute intensities, sometimes known as spin counting, is outside the scope of this SOP.
Materials
Definitions:
- CQ: Quadrupolar coupling constant
Appendix:
Using the tip angles above will result in a maximum integrated intensity deviation of 5% between a perfectly non-selective excitation and a perfectly selective excitation. As perfectly selective excitation is unlikely using these powers, the real deviation will likely be lower. This limit of 5% only applies to the homogeneity of the excitation and not other possible sources of error, e.g., background subtraction.
Troubleshooting
Before start
User should be familiar with the power limitations and duty cycle of the probe being used.
User should be familiar with the maximum safe spinning speed of the probe and rotor being used.
Accurate T1 relaxation times and calibrated pulse lengths must have been obtained prior to starting.
The expected amount of time to completion is highly sample-dependent and cannot be accurately estimated ahead of time.
Procedure
Load pulse sequence zg.
Set the relaxation time d1 to 5 × T1, where T1 is the largest value previously measured.
Set the pulse power plw1 to a previously optimized 90° pulse power.
Using a previously optimized 90° non-selective pulse length corresponding to pulse power plw1, calculate a pulse length corresponding to the nuclear spin number of the observed nucleus:
| Nuclear Spin Number | Tip Angle | Factor | |
| 3/2 | 18° | 0.20 | |
| 5/2 | 11° | 0.12 | |
| 7/2 | 8° | 0.09 | |
| 9/2 | 6° | 0.66 |
Note
These tip angles ensure a worst-case quantification error of 5% between a site with a CQ of 0 MHz and a site with a very large CQ. In most cases the error will be much less.
Set the pulse length p1 to the value calculated in Step 4..
Set the acquisition time aq to a sufficiently long value such that the FID is not truncated.
Ensure that the central transition approaches the infinite-spinning limit by optimizing the MAS rate.
Obtain a preliminary spectrum using a stable MAS rate.
Increase the MAS rate by a safe increment.
Note
If the MAS rate cannot be safely increased, consider changing to a probe with a smaller rotor diameter. Quantification cannot be assured if increasing the MAS rate increases the line width.
Compare the two spectra. If the linewidth has not changed,
If the spectrum at higher MAS rate has a higher linewidth, .
Acquire the spectrum until the signal-to-noise ratio is satisfactory for all resonances.
Process the spectrum while paying careful attention to background subtraction and baseline correction if necessary.
Obtain the relative intensities of the resonances via integration if well-resolved, or deconvolution if not.
Apply the satellite transition intensity correction described in Massiot et al.
Protocol references
Vega, A. J. Quadrupolar Nuclei in Solids. John Wiley & Sons, Ltd 2010-03.
Massiot, D.; Bessada, C.; Coutures, J. P.; Taulelle, F. A Quantitative Study of 27Al MAS NMR in Crystalline YAG. Journal of Magnetic Resonance (1969)1990, 90 (2), 231–242.
https://doi.org/10.1016/0022-2364(90)90130-2.