Phase sensitive COSY and NOESY
The TPPI technique (Time Proportional Phase incremantation) allows detection in a quadratic sequence. We may therefore solve the problem of the discrimination of the sign of the frequencies upon the detection of a free precession signal in an experiment of impulsional NMR There are other methods in the phase mode like the STATES technique where the detection is in simultaneous quadratic. It is easier to achieve a phased NOESY rather than a classical NOESY, because this technique is much more sensitive. Moreover, the correlation spots meaning a spatial vicinity are in the negative portion of the spectrum versus the correlation spots due to the spin-spin coupling.