Sample: 80% Benzene in acetone-d6

Record a ¹H-decoupled ¹³C spectrum.

The calibration of the ¹³C 90º pulse via the transmitter channel is performed using the standard ¹³C parameter set (the pulse program is zg0dc). It is also possible to perform the calibration recording ¹H-coupled ¹³C spectrum. A ¹³C spectrum is repeated varying the pulse width (p0 at high power level pl1) until maximum and null points are found. 

It is very important to use a long recycle delay, usually d1=5*T₁(¹³C) (d1=60 s).

On the other hand, we select a specific resonance to be monitored as a function of the pulse length.  From this resonance we define the phase correction (using the phase subroutine) and plot region (using the DefPlot button) to be monitored. o1 is set on-resonance of the selected signal.

Start acquisition executing the AU paropt program. Answer the questions as follows:
 
             Enter parameter to modify:             p0
             Enter initial parameter value:          2
             Enter parameter increment:             2
             Enter # of experiments:                  16
 
In this case, paropt automatically acquires 16 spectra while incrementing the parameter p0 from 2 usec to 32 usec.

Each spectra is automatically processed with the defined lb value (usually lb=2) and for each value of p0, only the spectral region defined above is plotted. All spectra appear side-by-side in the corresponding procno 999. The first maximum value must be the 90º proton pulse. However, more carefully calibration is performed when you get nul the signal. At this point, the pulse would correspond to a 180º pulse. Further nulling must occur at 360 degree.

A more detailed description in the AVANCE USER's MANUAL, chapter 5.3: 90 observe 13C pulse calibration.