Java Security Settings:
      This web page employs Java, which requires specific security settings for correct operation.
      If the applets on this page do not run correctly, consult the Virtual Chemistry Experiments FAQ
      or the Physlet Physics web site for establishing the correct security settings.

NMR Spectroscopy: Inversion Recovery Experiment

How does one experimentally measure T1?

Detection in NMR spectroscopy employs coils along the x and y axes and therefore detects changes in magnetization in the xy plane (Mx and Mx). There is no detection of magnetization along the z axis. Since T1 is the time constant for changes in Mz and there is no direct measurement of Mz, how can one determine T1?

The answer is that detection is indirect using the Inversion Recovery experiment. This experiment is simulated in the following exercise. Examine the steps in the experiment and observe the behavior of the magnetization. See if you can figure out how this experiment tracks changes in Mz without directly measuring Mz.

Exercise

The pulse sequence for the Inversion Recovery experiment is:       180ox - τ - 90ox - FID

In between the two pulses, the system is allowed to evolve for a time τ. This sequence is repeated many times using different values of τ. The resulting data involves a signal that varies with the frequency, f, obtained from the Fourier transform of the FID and the delay time τ. The data is thus a function of two variables (f and τ) and is thus a 2D NMR experiment.

This simulation lets you step through each component of the sequence, observing the effect on the bulk magnetization. Carefully examine the response of the system to each pulse. Vary τ between 0 and 10 sec and observe its effect on the spectrum. (Only the data after the vertical blue line is part of the FID and is put through the FFT to obtain the spectrum.)

Answer the following questions.

 

The steps of the simulation have been slowed, to varying degrees, to make visualization easier. The simulation time is plotted on the graph and shows the actual time scale for the experiment.

τ (sec) =
     
     

     



 


This page requires Java3D. If an applet on this page is not visible, consult the Java3D FAQ. Drag with the left mouse button to rotate, the center button to zoom, and the right button to move the object.


Spin Echo Experiment
Phasing the NMR Spectrum
NMR Spectroscopy Home Page
Virtual Chemistry Experiments Home Page


InversionRecovery.html version 1.1
© Copyright 2013-2014, David N. Blauch