The hetero-COSY block is the heteronuclear version of the conventional COSY block. It converts antiphase magnetization of the type I_yS_z into I_zS_y in a IS spin system by the simultaneous application of two 90 pulses on I and S spins, respectively. This block is usually found in the terminal part of, for instance, an INEPT block or the starting point in reverse INEPT block and related approaches. Closely related to this block is a zz-filter.

Easy implementation on AVANCE spectrometers.

The standard way to implement block (see hsqcph) is:

... (p1 ph2) (p3 ph3):f2 ...

in which:

• p1 is the high-power 90 pulse from the transmitter or f1 channel and p3 is the high-power 90 pulse from the decoupler or f2 channel.
• Phases are specified at the end of pulse program