Phase Cycling in INEPT

Note that the conversion S2 - Sx in the last step is brought about by the 90° 13C pulse only the 90° XH pulse has no effect on this conversion. The desired term, 4[—2S IZ], comes from 21 Sz and requires both 90° pulses, on and 13C, to be produced. Consider what happens if we change the phase of the 90° pulse from +/ to -y 

Only the 13 C 90° pulse operates on Sz to rotate it to Sx, so the phase of the H 90° pulse is irrelevant (Fig. 7.25, bottom left and bottom center). Now we can apply the phase-cycling strategy acquire one FID using the 11 90° pulse on +/ and a second FID with the 90° pulse on — /. Subtract the second FID from the first. The result will be  

Fourier transformation will give a spectrum corresponding to 8[—28 1 ] an antiphase 13C doublet with intensities of —8 = a component) and +8 = ft component) 

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