The WALTZ scheme is a composite pulse sequence highly advisable for broadband decoupling purposes. In addition, the rapid inversion of spins over its wide bandwith provides a good homonuclear Hartmann-Hahn match in the rotating frame for all resonances and induces magnetization transfer between coupled spins. This is the basis for the use of WALTZ sequences as a isotropic mixing in  TOCSY experiments (see The TOCSY block).

Easy implementation on AVANCE spectrometers.

It was devised that MLEV sequences were extremely sensitive to small errors in the rf phase shifts. Sequences which only use rf phases of 0 and 180 degrees are remarkably insensitive to errors in phase shifts. Thus, the basic and inverted element of the WALTZ sequence ( 83JMR335-52 and 83JMR313-53 ) is
    The most simple scheme is the WALTZ-4 (RRrr)

 

  However, the most used scheme is the WALTZ-16 in which the cycle QqqQ is repeated indefinitely.
 

WALTZ-16 appears adequate for proton decoupling in carbon-detected experiments and its operating bandwith is roughly DB=+-B2. Increased bandwith at the expense of poorer uniformity can be obtained using modified pulse lengths ( 85JMR113-62 ).

WALTZ scheme is also widely used for effective heteronuclear cross-polarization purposes ( 91JMR405-91 and 91JMR413-91 ).

Calibration of 90º and 180º pulses must be made at the required power. In general, for TOCSY applications, the power is adjusted to give a 90º pulse about 30-35 microseconds. A 10% variation in such calibrations could be tolerated.

For further experimental details, see the following tutorials:

• Tutorial: 90º ¹H observe pulse calibration.
• Tutorial: 2D TOCSY experiment.