Broadband ¹H decoupling is commonly used as the relaxation period in NMR experiments starting from a 90º pulse of a low-abundant nucleus, for instance, ¹³C, in order to improve the sensitivity by the NOE effect (see 90º ¹³C pulse). During this period, a WALTZ pulse train is applied to achieve polarization transfer from ¹H to ¹³C via the NOE effect. Such approach in not advisable for nuclei having negative magnetogyric ratios, for instance, ¹⁵N.

Easy implementation on AVANCE spectrometers. Broadband ¹H decoupling is achieved by defining a composite pulse decoupling (cpd) scheme in the acquisition parameters.

The duration of ¹H decoupling, d1,  is set to 1-5*T₁(¹³C) (in seconds) and it is very important to define the total experimental time of the NMR experiment to be recorded.

The standard way to implement broadband ¹H decoupling in a pulse program is:

... d12 pl12:f2 d1 cpd2:f2 ... d12 do:f2

The user must define:

• pl12 (or sometimes pl13) is the power level of the applied cpd sequence from the f2 channel.
• cpd2 is the pulse train to be applied (for instance, define cpdprg2=waltz16).
• pcpd2 is the the 90 degree pulse for decoupling sequence. Usually pcpd2 is set to 80 us that corresponds to the 90 degree pulse at a power level of pl12. See low-power 90º ¹H decouple pulse calibration for more details.
• When decoupling is applied it is very important in which stage of the pulse sequence it is stopped. This is made by executing the do:f2 command.

In all these cases, the overall pre-scan duration will be defined by the addition of all delays existing between the end of the FID acquition (see the go command) and the first pulse creating transverse magnetization.

See some examples: