Sample: 10% CHCl₃ in Acetone-d₆

Record a conventional ¹H spectrum.

The calibration of the 90º pulse via the transmitter channel is performed using the standard ¹H parameter set (the pulse program is set to pulprog zg). A ¹H spectrum is repeated varying the pulse width (p1 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(¹H) (d1=30 s).

Answer the questions as follows:
 
             Enter parameter to modify:             p1
             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 p1 from 2 usec to 32 usec.

Each spectra is automatically processed with the defined lb value (usually lb=1) and for each value of p1, 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 360º.
 
 

This calibration procedure can be repeated other power levels (pl1). For TOCSY-like applications, it is usually recommended to use a pl1 value giving a 90º observe proton pulse around 30-40 usec. On the other hand, ROESY-like experiments use a power level giving a 90º observe 1H pulse around 100-125 usec. To have a theoretical 90º 1H pulse value at a given power level, the pulse length is doubled each 6 dB and multiplied by 10 each 20 dB.

More detailed description in the AVANCE USER's MANUAL, chapter 5.2: 90 1H observe pulse calibration.