An interesting and simple approach to effective multiple-solvent suppression is proposed using the basic principles of the excitation sculpting methodology. Flat baseline and ultra-clean NMR spectra are usually obtained under standard conditions using a modified double pulsed field gradient echo scheme in samples containing mixtures of non-deuterated solvents. The simple performance of such an approach, the high tolerance to experimental mis-settings, the impressive level of solvent suppression and the easy incorporation of the proposed scheme in multi-dimensional NMR experiments make this method suitable for possible applications in liquid chromatography NMR. (C) 1998 John Wiley & Sons, Ltd.

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The behaviour of several recently proposed frequency-selective NMR excitation methods was monitored using brucine as a test sample. For each method the results were compared in terms of selectivity, sensitivity, phase properties and J-coupling refocussing. Methods using pulsed field gradients gave better overall results than shaped pulses alone. A slight modification of the WATERGATE method, incorporating the exclusive use of Gaussian pulses and the insertion of a final refocussing delay, gave the most satisfactory results.

This chapter presents the introduction of two-dimensional (2D) methods, specifically in the context of determining homonuclear correlations. This is so that the 2D concept is introduced with a realistically useful experiment in mind, although it also becomes apparent that the general principles involved are common to any 2D experiment. Following this, a variety of correlation techniques are presented for identifying scalar (J) couplings among homonuclear spins, which for the most part means protons although methods for correlating spins of low abundance nuclides such as carbon are also discussed. Thes chapter introduces the operation and use of pulsed field gradients. The techniques themselves begin with basic correlation spectroscopy (COSY), which maps nuclei sharing a mutual scalar coupling within a molecule, making the proton–proton COSY one of the workhorse techniques in organic structure elucidation. In the chapter, some variants of the basic COSY experiment that display a number of beneficial characteristics are presented. The chapter discusses techniques such as total correlation spectroscopy (TOCSY), which provides an alternative to the COSY approach for establishing correlations within a molecule. This provides efficient transfer of information along a network of coupled spins, a feature that can be extremely powerful in the analysis of more complex spectra. The final method—incredible natural-abundance double-quantum transfer experiment (INADEQUATE)—establishes correlations between like spins of low natural abundance.