Sample: Lineshape test sample (for instance, 3% CHCl₃ in acetone-d₆). Alternatively, a 100mM Urea ¹⁵N, 100mM CH₃OH ¹³C in DMSO-d₆ sample can also be used

Perform the high-power 90º ¹³C decoupler pulse calibration, if required.

The calibration of the low-power 90º ¹³C pulse via the decoupler channel (for GARP composite pulse decoupling (cpd)) is performed using the same parameters as described for the analogous high-power 90º ¹³C decoupler pulse calibration (the pulse program is decp90) in which a 90º ¹³C pulse length about 80 usec is required. 

Use the same values:

p1=high-power 90º ¹H observe pulse

d2=1/2*J_CH=2.33ms

ns=1

It is very important to use a long recycle delay, usually d1=5*T1(¹H) (d1=20 s).

The CHCl₃ resonance is 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 a value of p3=80us at a very low power level pl2 (try a starting power level of 40 dB, for instance). After proper phasing, the first spectrum shows an up-down doublet for the satellites resonances. Repeat the experiment increasing the value of pl2 until a nul point for the satellites is achieved (this is the 90º ¹H decoupler pulse). When pl2 reachs 180º degree, the satellites shown a reverse down-up pattern..

Use standard ¹H processing parameters (efp with lb=1).

The parameters used by cpd sequences are pcpd2 for the 90° pulse length and pl12 for the decoupler power level, rather than p3 and pl2 as used here.

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