4. Acquisition

Time requirement: 20 min

Sample: 10% CHCl₃ in [D₆]acetone with added Cr(acac)₃.

Set the instrument to normal ¹H NMR operation, obtain a good homogeneity and load a pulse program as shown above. You have to set:

td	4 k
sw	500 Hz
o1	on resonance of CHCl₃ signal
p1	30° ¹H transmitter pulse
d1	5 s
d2	gradient ring-down delay [100 μs]
g1	positive pulsed field gradient, approximately 0.1 T/m, duration 1 ms, sinusoidal shape
g2	negative pulsed field gradient, approximately 0.1 T/m, duration 1 ms, sinusoidal shape, strength to be varied
ns	1

First record an ¹H NMR spectrum with identical gradients but of opposite sign. Vary the strength of the second gradient within a ±1% range of the first and note the signal change. Use other strengths and shapes for both gradients to study the influence of these parameters.

5. Processing

Use standard ¹H processing as described in Experiment 3.1 with an exponential window (lb = 2 Hz).

6. Result

The figure shows a series of signals obtained on an AMX-500 spectrometer with a BGU (10 A) gradient unit and an inverse gradient probe-head with self-shielded gradients. g1 was set to +50.0 (relative units) and g2 was varied in steps of 0.1 from −49.7 to −50.3. Note that the result is slightly asymmetrical and that therefore the zero point of the gradient amplifier has to be more carefully adjusted.