NMR π/2 Pulse Calibration Experiment

. This experiment was developed by S.E. Van Bramer for Chemistry 465 at Widener University.

Introduction:

This experimental procedure is for finding the π/2 pulse angle for an NMR spectrometer. This experiment shows how the sample is perturbed from equilibrium by the initial pulse. In subsequent experiments we will study how the sample returns to equilibrium through T1 and T2 relaxation. The π/2 and pulse angles are very important for these latter experiments and it is also a useful diagnostic for monitoring the transmitter power. The experimental details outlined here are in addition to the basic steps outlined in "NMR Operations for QE-300" and this should be treated as a supplement to that document.


Experimental:

Typographic Conventions

  1. Special keys are written out, press the key shown, ie: <return> means to press the key that says "return".

  2. Most commands are entered as 2 letter commands. These commands are represented here as bold caps in brackets ie [EJ]. They are entered without a <return>.

  3. Some sequences require holding the control key and pressing an additional key. [^W] means hold the <control> key and press W.

  4. Additional comments are made in italics.

  5. A sequence of keystrokes or commands is separated by commas.

Safety

  1. DO NOT ENTER KB 421 if you have a pacemaker or other metal implant.

  2. DO NOT place any magnetic material near the magnet.

  3. DO NOT drop small metal material in the room.

  4. DO NOT bring large metal objects into KB 421.

  5. Credit Cards, Computer Disketts, and ATM cards can be erased inside the yellow warning rope.

  6. DO NOT work unsupervised

  7. Follow Directions and Ask questions. The NMR costs about $150,000, be careful

  8. Sign-in the logbook

Sample Preparation

Sample Loading

Setup the Magnet For The New Sample

Setup Computer for Experiment

  1. Select the Current Nucleus. [CN]

  2. Set the Pulse angle to 90D. [P2], 90D, <return>

  3. Set the Receiver Gain. [SG]

  4. Set Number of Acquisitions. [NA] (Start with 1, increase to improve S/N, use multiples of 8 for proper phase cycling.)

  5. Set the Block Size (suggest 16k for 1-H, 32k for 13-C). [CB]

  6. Collect a spectrum to test your settings
    1. Transform the spectrum [FT].
    2. Zoom in and reset the spectrometer to observe the selected region. [OW]
    3. Select absolute intensity mode. [AI]

  7. Select the Pulse List experiment: [EX], PLIST, <return>
    1. P4 is the list of acquisition pulses (in microseconds). Enter a list of values (NOTE: a π/2 pulse is approximately 12 microseconds). End the list by imputing a value of 0.
    2. D5 is the recycle time. Set D5 > 5 T1. (Note: this is important, if D5 is too short the experiment will saturate.)

  8. Collect Data and save in a sequence of files. [GS] (This will sum [NA] FID's for each value of P4. Each FID is saved with a different file name by incrementing the extension.)

  9. Set the phase correction.
    1. Open File for a pulse width close to π/2. [GA]
    2. Baseline Correct the FID. [BC]
    3. Exponential Multiplication (optional to improve S/N) [EM]
    4. Fourier Transform FID. [FT]
    5. Autophase Spectrum. [AP]

  10. Process the FIDs (This may be easily automated to process data in NUTS)
    1. Open the FID File. [GA]
    2. Baseline Correct FID. [BC]
    3. Exponential Multiplication (optional to improve S/N) [EM]
    4. Fourier Transform FID. [FT]
    5. Phase Spectrum with saved values. [PS]
    6. Determine the peak height. [YS], [PP]
    7. Save Spectrum in new file [SA]

Create a Stacked Plot for the Experiment

  1. Import the spectrum closest to the π pulse. [GA]

  2. Set the Y-Scale. [YS]

  3. Import the spectrum closest to the 3/2 π pulse and set the scaling. [PP], [P]

  4. Check Offsets by plotting to the Video. [SV]

  5. Adjust Offsets as necessary. [PO] (values for X & Y offsets in mm, suggest Y- Offset of 0 mm and X-Offset 10 mm)

  6. Plot the spectra. [SP] (enter filename of first spectrum)

Repeat with different spectrometer frequency setting


Laboratory Write-up:

Your Laboratory write-up should include the following information
  1. An Abstract of your experiment.

  2. The Carbon pages from your laboratory notebook.

  3. A Stacked Plot of your spectral data.

  4. Graph the peak intensity vs time

  5. Determine the π/2 pulse width

  6. Based on the π/2 pulse width, what is the bandwidth of the acquisition pulse.


This page is maintained by
Scott Van Bramer
Department of Chemistry
Widener University
Chester, PA 19013

Please send any comments, corrections, or suggestions to svanbram@science.widener.edu.

This page has been accessed 589 times since 1/5 /96 .
Last Updated Sunday, August 18, 1996 7:15:57 PM