Solvent suppression methods

On-line coupling of separation techniques to NMR has recently been reviewed [459,651-653], and solvent suppression methods in NMR spectroscopy in particular [654],... 

A solvent-suppression method is normally required in NMR applications because the solvent signals, if not suppressed, may saturate the receiver and hinder... 

Mohebbi and Shaka (1991b) also developed selective homonuclear Hartmann-Hahn experiments based on zero-quantum analogs of DANTE sequences (Bodenhausen et al., 1976 Morris and Freeman, 1978) and binomial solvent suppression methods (Plateau and Gueron, 1982 Sklenaf and Starcuk, 1982 Hore, 1983) (see Section X.C). 

The area of solvent suppression has a long history and is an indispensable part of almost every NMR experiment conducted in a solvent containing nuclei of the type to be detected. This chapter provides a general coverage of solvent suppression methods in NMR with special attention to the enormous developments in the past decade that have occurred due to the... 

One of the most commonly encountered questions is "How long do I have to wait until my sample reaches equilibrium " This is just as important for high throughput studies such as metabonomics and medical diagnostics that use only a few scans as it is for multidimensional biomolecular studies where a single experiment can last up to 6 days. The answer (and solvent suppression method) depends on the application. 

It has always been desirable to have an analytical process for the evaluation of solvent suppression methods. One of the first attempts at quantitation was done by Peter Hore in his review of solvent suppression. However, it has been difficult to establish a method for the same reasons that solvent suppression is difficult in the first place. Each solvent behaves differently in terms of relaxation, coupling, and chemical shift (among other properties). In addition, each spectrometer has different characteristics and each user individually evaluates the quality of shimming to be used and the time available for optimizations. This makes establishing a standard sample to work on and how any pulse sequence will be evaluated challenging (to say the least). 

Four general classes of NMR experiments are routinely used to analyze metabolites (1) ID NMR experiments (2) 2D NMR experiments (3) Solvent suppression methods and (4) Hyphenated NMR experiments. The ID and 2D NMR experiments are commonly used for metabolite structure determination. The various solvent suppression techniques (Gaggelli and Valensin, 1993 Hwang and Shaka, 1995 Smallcombe and Patt, 1995) are crucial for dilute metabolite samples where the solvent peak is the most intense peak in the NMR spectrum. These solvent suppression techniques can be incorporated as needed in both ID and 2D NMR experiments. Since their introduction in the 1990s, hyphenated NMR methods have become common tools in the identification of metabolites. These methods include LC-NMR (Albert, 1995 Spraul et al., 1993, 1994), LC-NMR-MS (Mass Spectrometry) (Shockcor et al., 1996) and LC/SPE (solid phase extraction)/NMR (Alexander et al., 2006 Bieri et al., 2006 Xu et al., 2005 Wilson et al., 2006). 

One practical outcome of these improved solvent suppression methods is that it has now become important to suppress the satellites of the solvent signal as these may be the largest signals left in the spectrum after the suppression of the solvent signal [131]. 

In 1996, Whittenburg presented a solvent suppression method using Bayesian analysis methods but which assumes the solvent peak to have Lorentzian lineshapc. 

See also Diffusion Studied Using NMR Spectroscopy NMR Pulse Sequences Product Operator Formalism in NMR Solvent Suppression Methods in NMR Spectroscopy Two-Dimensional NMR, Methods. 

Owing to the limitation of space, this article focuses on the introduction of general principles of the solvent suppression methods, and emphasizes some of the important developments. The reader is encouraged to refer to the original literature and recent reviews for the fundamentals and details of the methods. 

See also NMR Pulse Sequences Nuclear Overhaus-er Effect Proteins Studied Using NMR Spectroscopy Solvent Suppression Methods in NMR Spectroscopy Structural Chemistry Using NMR Spectroscopy, Organic Molecules Structural Chemistry Using NMR Spectroscopy, Pharmaceuticals Two-Dimensional NMR Methods. 

In the late 1970s and early 1980s, a number of attempts to couple these techniques were carried out. However, these studies suffered from the low sensitivity of the NMR spectrometer systems then available. Also, because of dynamic-range problems, there was a need to use expensive deuterated solvents for the HPLC because the solvent suppression methods in use at the time could not cope with fully protonated solvents. The reduction of HPLC-NMR to routine use was slow in developing and not practically achieved until technical improvements in electronics, higher magnetic fields strengths, advanced solvent suppression sequences, and improved instrumental sensitivity, made it feasible to interface an HPLC directly to an NMR spectrometer. 

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