Sample: 80% benzene in acetone-d₆

Record a conventional ¹H spectrum.

Record a ¹H-coupled ¹³C spectrum.

The calibration of the 90º ¹H pulse via the decoupler channel is performed using the standard ¹³C parameters (the pulse program is decp90). 

The initial values are p1=90º ¹³C observe pulse at high power level pl1, d2=1/(2*J_CH) and ns=1. It is very important to use a long recycle delay, usually d1=5*T1(¹³C) (d1=60 s).

o1 and o2 are set on-resonance of the selected ¹³C and ¹H resonances, respectively.

using an initial value of p3=0us at high power level pl2. Repeat the experiment increasing the value of p3.

Use standard ¹³C processing parameters (efp with lb=2). After proper phasing, the first spectrum shows an up-down doublet. When p3 is increased, the signal intensity of this antiphase signal is decreased until a nul point is achieved (this is the 90º ¹H decoupler pulse). When p3 reachs 180º degree, an antiphase ¹³C resonance in a reverse down-up mode is obtained.

PLOT

The same procedure is used to calibrate the 90º ¹H decouple pulse at other lower power levels pl2. For instance, for WALTZ (or DIPSI) ¹H decoupling during ¹³C or X acquisition, a power level giving a 90º ¹H pulse around 80-100 usec is usually chosen. On the other hand, for high selective pulses a closely related experiments is also described (see selective 1H Decouple 90° pulse calibration).

The 1H Decouple 90° pulse calibration can also be performed optimizing the DEPT-90 pulse sequence.

A more detailed description in the AVANCE USER's MANUAL, chapter 5.4: 1H Decouple 90° Pulse .