The probe-head should be tuned to the sample. Load standard ¹³C parameters with ¹H broad-band decoupling, record a normal ¹³C NMR spectrum and note the offset of CHCl₃. 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 ¹³C signal
o2	middle of ¹H NMR spectrum
p1	¹³C transmitter pulse, 7 μs for experiment a and 14 μs for experiment b
d1	60 s
rg	receiver gain for correct ADC input
decoupler attenuation and 90° pulse duration for composite pulse decoupling (CPD)
ns	1

Record spectrum a with p1 = 7 μs and spectrum b with p1 = 14 μs. Note the heights I₁ and I₂ of the CHCl₃ signal in these two spectra. If the pulse-width in the second experiment is double that in the first experiment, Equation (1) holds, from which the pulse angle α₁ (in degrees) of the first experiment can be calculated:

α₁ = arccos (0.5I₂ / I₁)(1)

Using Equation (2) the 90° pulse-length p₉₀ can be calculated, where p1 is the pulse-length of the first experiment. p₉₀ should be checked by applying the corresponding 180° pulse.

p₉₀ = 90p1/α₁(2)

5. Processing

Use standard 1D processing (see Exp. 3.2) applying an exponential window with a line-broadening factor lb = 1 Hz. Adjust the phase of the first spectrum for absorption and use the same phase correction for the second experiment.

6. Result

Two-point carbon-13 pulse calibration spectra