Practical implementation of PFGs

One final point regarding field gradients is worthy of note. Since a gradient pulse induces a spatially dependent phase for all magnetisation in the sample, this also leads to 

This then finishes this part of the chapter that has essentially laid the foundations for understanding 2D (or more generally nD) NMR. Throughout this, the basic COSY sequence, either in its absolute-value or phase-sensitive forms, has been used as an illustrative 2D sequence. Not only is COSY a simple sequence, but the spectra are rather easy to interpret and require relatively little explanation. Beyond this basic sequence, there are various other COSY experiments that provide the chemist with new or modified information. These are, in fact, more widely used in the laboratory than the experiment described thus far, and it is these that are now addressed before progressing to consider other homonuclear correlation techniques. 

As simple as this scheme may sound, it is plagued by a number of technical problems that would make the collection of high-resolution data impossible if left unchecked, and it is these problems that slowed the introduction of field gradients in high-resolution NMR for so long. The worst of these are the eddy 

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