A single PFG inserted into two 90° pulses selects coherence order p=0 during the filter delay whereas residual transverse magnetization is dephased.  

A particular case should be the mixing time in NOESY experiments (see the NOESY block).

Easy implementation on AVANCE spectrometers equipped with gradient technology.

In general, the only parameter to define in a z-filter is the gradient strength of the involved gradient that must avoid undesired refocusing effects with other gradients applied during the pulse sequence.

The standard way to implement a z-gradient filter in a pulse program is:

... p1 ph1 d13 p16:gp1 d16 p1 ph2 ...

in which:

• p1 is the high-power 90 degree pulse of the nucleus involved (in this case applied from the f1 channel)
• p16 is the duration of the gradient (in microseconds)
• d16 is the recovery time (in seconds) needed after the gradient
• gp1 is the gradient strength defined in the gpz1 command. Otherwhise, gpnam1 defines the shape of the gradient.