Sample: 100mM Urea ¹⁵N, 100mM CH₃OH ¹³C in DMSO-d₆

The calibration of the low-power 90º ¹⁵N pulse via the decoupler channel (for GARP composite pulse decoupling (cpd)) is performed using the same parameters as for the analogous high-power 90º ¹⁵N decoupler pulse calibration (the pulse program is decp90) in which a 90º ¹⁵N pulse length about 180-200 usec is required.  For the calibration of this pulse from the f3 channel, you must use:

Use the same values:

p1=high-power 90º ¹H observe pulse

d2=1/2*J_NH=5.649ms for 88.5 Hz.

ns=1

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

The urea 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 ¹⁵N (76 ppm) resonances, respectively.

Start acquisition with rga and zg using a value of p3=180-200us at a very low power level pl2 (try a starting power level of 30 dB, for instance). After proper phasing, the first spectrum shows an up-down doublet for the urea resonance near to 5.45 ppm. Repeat the experiment increasing the value of pl2 until a nul point for the doublet is achieved (this is the 90º ¹⁵N decoupler pulse). When pl2 reachs 180º degree, the doublet shown a reverse down-up pattern.

Use standard ¹H processing parameters (efp with lb=0.3).

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.

For a three channel system calibrate also the 90 degree pulse for the third channel with decp90f3. Use all necessary filters.