Feb 17, 2025
Version 1
Quadrupole Non-Selective Pulse Width Optimization 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. Quadrupole Non-Selective Pulse Width Optimization. protocols.io https://dx.doi.org/10.17504/protocols.io.4r3l29y2jv1y/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. We intend to publish it in June 2025.
Created: February 11, 2025
Last Modified: February 17, 2025
Protocol Integer ID: 119905
Keywords: Materials Non-Selective Pulse Width Optimization: 23Na, quadrupolar nucleus, low quadrupolar coupling constant, standard sample with high sensitivity, pulse width, solid sample with negligible cq, standard sample, solid sample, high sensitivity, calibration
Funders Acknowledgements:
National Science Foundation
Grant ID: 1946970
Abstract
Purpose
Calibration of non-selective 90° pulse width using a standard sample for a quadrupolar nucleus.
Scope
This protocol uses a standard sample with high sensitivity and low quadrupolar coupling constant. This can be a solid sample with negligible CQ (e.g., NaCl for 23Na) or a solution sample (e.g., 1 M NaCl for 23Na).
Guidelines
This SOP should be among the first executed when investigating a new sample.
This SOP is written to the level of an experienced NMR spectroscopist who is unfamiliar with the acquisition of spectra from quadrupolar nuclei.
Calibration and validation of a central transition-selective pulse is outside the scope of this SOP; CT-selective pulses should be calibrated on the sample of interest using SOP Materials Central-Transition-Selective Pulse Width Optimization.
Materials
Definitions:
- CT: Central Transition
- CQ: Quadrupolar coupling constant
Appendix:
The 360° zero crossing is less reliable in half-integer quadrupoles than in spin-1/2 nuclei. The 180° zero crossing point is preferred.
The nutation curve of will be non-sinusoidal if the relaxation delay d1 is too short; however, the 180° zero crossing should be reliable regardless of precise relaxation time.
Troubleshooting
Safety warnings
User should be familiar with the power limitations and duty cycle of the probe being used.
Before start
This protocol is intended for a high-symmetry standard sample with low CQ, such as NaCl for 23Na. A 1 M solution of an appropriate salt can also be used.
Probe must be well-tuned and well-matched.
SOP written for Bruker spectrometers.
Expected completion time: <1 hour
Procedure
Open a new experiment window and load the zg pulse sequence.
Load previously known good pulse length p1 and pulse power plw1.
Note
If previously known good values aren't available, a reasonable starting point is a 1 μs pulse using a power level from a nearby nucleus, e.g. 13C and 23Na.
Safety information
If there is no information at all on previously known pulse lengths and powers in this frequency range, consult the local expert responsible for the probe being used. If you are that expert and need guidance, consult with the probe vendor.
Acquire an initial spectrum and ensure that there is adequate signal. If signal is inadequate, increase the number of scans and repeat this step.
Open a popt window.
Array pulse width p1 from 1.0 μs to 8 μs in steps of 0.5 μs. There should be 15 experiments.
Run the popt and observe the nutation curve.
Determine the 90° pulse length by finding the pulse length corresponding to the 180° zero crossing point and dividing it by 2.
If a more accurate determination is required, popt can be run again with revised start, end, and step values.
Set p1 to this value.
If a particular radiofrequency power is desired, use the pulse au program to estimate the amplifier power required and optimize the pulse power plw1 using popt.
Confirm the pulse power limitations of the probe prior to optimizing plw1 and ensure that the optimization routine will not allow for the power limit to be exceeded.
Repeat this protocol until the pulse length and power are optimized to the level required.
Protocol references
Wasylishen, R. E.; Ashbrook, S. E.; Wimperis, S. NMR of Quadrupolar Nuclei in Solid Materials; WILEY, 2012-08-07.