Sample: Lineshape test sample (for instance, 3% CHCl₃ in acetone-d₆)

Record a conventional ¹H spectrum..

In a new dataset record a ¹H-decoupled ¹³C spectrum.

From the preliminar 1H spectrum, creates a new data set with edc. The calibration of the 90º ¹³C pulse via the decoupler channel is performed using the standard ¹H parameters (the pulse program is decp90) and defining NUC2=13C in edsp. 

The initial values are p1=90º ¹H observe pulse, d2=1/2JCH=2.33ms and ns=1. It is very important to use a long recycle delay, usually d1=5*T1(¹H) (d1=20 s).

On the other hand, we select the CHCl₃ 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 and o2 are set on-resonance of the selected ¹H and ¹³C resonances, respectively.

Start acquisition with rga and zg using an initial value of p3=0us at high power level pl2. Repeat the experiment increasing the value of p3.

Use standard ¹H processing parameters (efp with lb=1). After proper phasing, the first spectrum shows an up-down doublet for the satellites resonances. When p3 is increased, the signal intensity of this antiphase signal is decreased until a nul point for the satellites is achieved (this is the 90º ¹H decoupler pulse). When p3 reachs 180º degree, the satellites shwon a reverse down-up pattern.

The same procedure must be used to calibrate the 90º ¹³C pulse using other power levels. For instance,  GARP decoupling requires a 90° decoupling pulse length of 60 to 70 usec. Note that the parameters used by cpd sequences are pcpd2 for the 90° pulse time and pl12 for the decoupler power level, rather than p3 and pl2 as used here.

On the other hand, an 1D ¹³C-coupled HMQC experiment is recorded to check the calibrated pulses (see AVANCE USER's MANUAL, chapter 5.5.4).

A more detailed description in the AVANCE USER's MANUAL, chapter 5.5: 90 13C decouple pulse calibration.