180º pulses placed into heteronuclear pulse sequences can be used to refocuse a desired chemical-shift, homo- or heteronuclear J-coupling information, depending of the position into the pulse sequence and on the nuclei that they are applied.

If refocusing 180º pulses are applied on both ¹H and ¹³C nuclei, both ¹H and ¹³C chemical shifts are refocused at the end of the echo period while ¹H-¹H and  ¹H-¹³C coupling constants are not affected.
 

Some typicals examples are:

The variable heteronuclear spin-echo t₁ period.

The fixed evolution periods in INEPT, refocused INEPT pulse trains or related HSQC experiments.

Easy implementation on AVANCE spectrometers.

There are 32 duration parameters, d0-d31,  to be specified in seconds. They are executed as delays without any further actions by the pulse program commands d0. They can be incremented or decremented using the pulse program commands id0-id31 or dd0-dd31, respectively. The changes are given by the parameters IN0-IN31. The pulse program commands rd0-rd31 reset a respective delay to its original value. The delays may also be changed by means of arithmetic expressions during pulse program execution.

The standard way to implement an heteronuclear spin-echo period in a X-detected experiment is:

... d4 (p2 ph1) (p4 ph2):f2 d4 ...

in which:

• d4 is the evolution delay optimized to 1/(4*J_XH) (in seconds).
• p2 is the 180º X  pulse (in microseconds) applied at a power level pl1 from the f1 channel. p4 is the 180º ¹H pulse (in microseconds) applied at a power level pl2 from the f2 channel. Note: In a 1H-detected experiment (see hsqcgpph) the two channels are exchanged.
• All phases may be specified at the end of pulse program.