Sample: 10% CHCl₃ in [D₆]acetone; do not use a degassed and sealed sample, since that would make the relaxation time of the CHCl₃ protons exceedingly long.

The probe-head should be tuned to the sample. Load standard ¹H parameters, record a normal ¹H NMR spectrum and note the offset of the CHCl₃-proton. On older instruments change to the absolute intensity mode. You have to set:

transmitter attenuation [3 dB]
td	4 k
sw	500 Hz
o1	on resonance of CHCl₃ signal
p1	¹H transmitter pulse, to be varied, 1 μs as initial value
d1	30 s
rg	receiver gain for correct ADC input
ns	1

Increase p1 in 2 μs steps until the intensity of the processed signal begins to drop to nearly zero. Now use smaller steps in increasing p1, e.g. 0.1 μs, to find the minimum for the 180° pulse. With the determined pulse-length check the 90° pulse (maximum positive intensity), the 270° pulse (maximum negative intensity) and the 360° pulse (minimum intensity). If there are small deviations, calculate an average value for the 90° pulse-length. In case of large deviations repeat the procedure. If the deviations are still present, the probe-head may be arcing; increase the transmitter attenuation.

5. Processing

Use standard 1D processing (see Exp. 3.1) applying an exponential window with a line-broadening factor lb = 1 Hz. Adjust the phase of the first spectrum for pure absorption and always use the same phase correction.

6. Result

Sinusoidal proton signal intensity versus pulse width