The 15N pulse calibrations should be done in the inverse mode (15N through the 3rd channel) using the pulse sequence decp90f3 (see Tutorial: Pulse Calibrations) . For instance, a sample of 0.1 M Urea-15N in DMSO-d6. can be used. The 15N-offset for the amide groups in urea is 76 ppm, the amide 1H-offset is 5.4 ppm and the one-bond coupling constant is 89 Hz. The calibration affords an antiphase signal that its intensity depends on the flip angle of the selective 15N-pulse. When the 15N-pulse is a perfect 90-pulse, the magnetization is completely converted to a multiple quantum coherence and the obseved signal reaches its minimum.
The required pulses to be applied from the 15N or f3 channel are:
15N 90 (p21) and 180 (p22) hard pulse at high power level (pl3) 15N 90 decoupling pulse (pcpd3=200us) at power level (pl16) using the scheme specified in cpdprg3=garp.