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.
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.
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