Solvent suppression in Fourier transform nuclear magnetic resonance

Digitisation and data processing in Fourier transform NMR

Publisher Summary This chapter discusses the practical advantages and disadvantages of the major methods of solvent suppression, without going into the theory behind them. The emphasis is on techniques developed during the past 5 years; earlier methods have been extensively reviewed elsewhere. Although the chapter shall concentrate on water suppression, most of the methods are applicable to other solvents and other nuclei. The majority of the above techniques can be used for 2D NMR. The most popular and satisfactory approach is presaturation; alternative methods are only worth considering if resonances of interest are attenuated by saturation transfer, cross-relaxation, or direct saturation. The most obvious method of water suppression is to use deuterium oxide (D 2 O) in place of H 2 O. The major problem is that labile NH and OH protons exchange for deuterons and hence disappear from the spectrum. Two older techniques are tailored excitation and rapid scan correlation. Neither is straightforward to implement and nor has been widely used for solvent suppression. The problems associated with double resonance (for selective decoupling and NOE measurements) in conjunction with solvent suppression can be circumvented to a large degree by two-dimensional methods (COSY and NOESY).

[3] Solvent suppression

Chromatography is nearly always the method of choice for the analysis of complex mixtures. Chromatography alone, however, is often inadequate; it is frequently necessary to use a hyphenated procedure in which chromatography is used for separation of the mixture into pure substances and then mass spectrometry, infrared spectroscopy, or some other spectroscopic method is used for structural identification of each component. Although nuclear magnetic resonance (NMR) spectroscopy has been very successful in structural determinations of pure compounds, it is seldom used for identification of specific molecules in complex mixtures. Here the authors show that methodology recently developed in their laboratory increases the power NMR for analysis of complex mixtures. They wish to emphasize that, because of the low sensitivity of NMR spectroscopy, the large amounts of material required for an analysis will restrict the applicability of the methods presented below. Nevertheless, the examples in this report illustrate the many important analytical problems that can be solved by means of ultra-high resolution NMR methods.

Ultra-high resolution NMR

Coupling of hplc and NMR. 2. Analysis of flowing liquid chromatographic fractions by proton magnetic resonance in the presence of hydrogen-containing eluting solvents

Ian S Mackay

Papers

Computers in NMR. IV. Strategies in developing high-dynamic-range fourier transforms