Other Variants of COSY

COSY can be combined with a z filter (see Section 9.5) into z-COSY, which is occasionally used to produce absorption phase spectra. A 90°, T, 90° sequence replaces the second 90° pulse in the usual COSY sequence, just as in DQF-COSY (see Fig. 12.6a). In this case, however, pulse 2 rotates in-phase magnetization to the z axis, where it is stored for the short r period and restored to the xy plane by pulse 3. Suitable phase cycling or imposition of a pulsed field gradient eliminates the coherences remaining in the xy plane during r, so that the final 

A variation of COSY called RELAY has been used to relay coherence from one coupled set of spins to a second set. RELAY employs a pulse sequence of 90°, r, 180°, t, 90° in place of the usual 90° mixing pulse. Although this method can be useful, it has largely been supplanted by TOCSY-HOHAHA, as described in Section 10.2. 

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