Absolute-value COSY

Figure 5.54. The absolute-value COSY-45 spectrum of 5.1 compared with the equivalent COSY-90 spectrum. The tilting apparent on some COSY-45 crosspeaks can indicate whether the active coupling arises from protons sharing geminal or vicinal relationships which produce peaks with positive and negative slopes respectively (see text).

There are several reports dating from the 1980s where metabolic analyses were performed with In a study by Alonso et al. absolute-value COSY... 

The COSY experiment can be either phase sensitive or nonphase sensitive (a.k.a. absolute-value COSY). The total integrated volume of a phase-sensitive COSY cross peak will always be zero because the cross peak will be composed of an equal distribution of positive and negative components. Phase-sensitive COSY spectra are useful for the measurement of 1-couplings between spins. 

To illustrate the incorporation of PFGs into conventional experiments, the basic COSY sequence is again used as an example. It has already been shown that for the absolute-value COSY experiment, those signals to be retained in the final COSY spectrum follow the coherence transfer pathway illustrated in Fig. 5.38, with N-type selection being the favoured option. For signal selection, it is sufficient to phase-encode coherences before the second 90° pulse and decode these after the pulse, immediately prior to detection. For... 

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