A hard 180_x inversion pulse can be replaced by a composite pulse consisting of the 90_x180_y90_x element. This is usually applied on the 180 X pulse of the 1H-X INEPT or DEPT tranfers in multidimensional NMR experiments in order to improve the inversion profile and the inhomogeneity of this pulse. See for instance deptcp, hxcocp.

Easy implementation on AVANCE spectrometers.

A typical 180 pulse is written as:

...
p4 ph1
...
ph1=0

In this case, the composite inversion element would be:

...
p3 ph1
3u
p4 ph2
3u
p3 ph1
...
ph1=0
ph2=1
or ...
(p3 ph1 3u p4 ph2 3u p3 ph1) ...
ph1=0
ph2=1

where p3 and p4 are the 90 and 180 pulses. When placed this inversion element into the INEPT pulse train, the following is written:

...
(p3 ph1 3u p4 ph2 3u p3 ph1):f2 (d21 p2 ph3) ...
ph1=0
ph2=1
ph3=0

where p2 is the 180 1H pulse and d21=(p3*2+6u-p2)/2