Nuclear magnetic resonance sensitivity enhancement

Bowers, C. R., Sensitivity enhancement utilizing parahydrogen. In Grant, D.M., Harris, R. K. (Eds.), Encyclopedia of Nuclear Magnetic Resonance, Volume 9, 2002, p.l. 

Chemiluminescence is a very sensitive and selective technique. Reagent types, analytes, and detection limits have been summarized in a review by Imai.56 Chemiluminescence has been applied to the analysis of compounds that exhibit low UV absorbance, including metal ions, amino acids, fatty acids, and bile acids. Other detectors include detectors for radioactivity, nuclear magnetic resonance (NMR), and surface-enhanced Raman spectroscopy. Radioactivity detection is one of the most selective detectors, as only components that have been radiolabeled will be detected. The interface of NMR with HPLC and has been discussed in detail by Grenier-Loustalot et al.57 Surface-enhanced Raman spectroscopy is another technique that... 

An extremely sensitive technique able to detect the nature of radical pairs in a photochemical reaction is called chemically induced dynamic nuclear polarization (CIDNP), which depends on the observation of an enhanced absorption in a nuclear magnetic resonance (NMR) spectrum of the sample, irradiated in situ, in the cavity of a NMR spectrometer. The background to and interpretation of CIDNP are discussed by Gilbert and Baggott (28). 

On the other hand, the spectroscopic techniques probe individual ionic species which build up the ionic aggregates. These techniques permit the investigation of the immediate chemical environments, the mobility of cations and water-ions Interactions. Metal nuclear magnetic resonance and Mossbauer spectroscopy are sensitive probes of counter cations and provide valuable information on the cations and their environment. Infrared spectroscopy is complementary to the above methods and addresses itself to the bound SO3" anions or water and the interaction of water molecules with the various species with which it is in contact. A common conclusion that is reached in the above mentioned studies is that four or five water molecules are needed to complete the hydration process. Reducing the level of moisture content (which surrounds the ionic species) below four water molecules per unit SOj site enhances the Coulombic interaction between the ionic species. This eventually leads to the formation of ion pairs in the dry membranes. These ion pairs do not necessarily disperse homogeneously in the fluorocarbon matrix but tend to form aggregates, phase separated from the matrix materials as demonstrated in the scattering studies. 

Resolution and sensitivity are essential to the collection of analytical chemical data with accuracy and precision. It is well known that mathematical transformation techniques enhance the resolution and sensitivity of spectroscopic methods. Fourier transform (FT), cross correlation (CC), and Fladamard transform (FIT) techniques allow for high resolution and high sensitivity of infrared spectroscopy (IR), fiuorometry, nuclear magnetic resonance... 

In more recent years, it has become less essential to use radioactivity, which, though very useful, is also hazardous. As we have mentioned, there are also stable, rare isotopes. In the case of hydrogen we have deuterium in the case of carbon we have carbon 13 (seven neutrons). It is also possible to label a biochemical compound with a stable isotope. Some of these isotopes ( C being one) can be monitored by nuclear magnetic resonance (NMR) all of them can be detected by mass spectrometry, which, as the name implies, relies on measuring the differences in mass of different molecules or fragments of molecules. The improved sensitivity of these two techniques in recent years has enhanced the usefulness of stable isotopes. 

Lerner L, Bax A (1986) Sensitivity-enhanced two-dimensional heteronuclear relayed coherence transfer NMR spectroscopy. J Magn Reson 69 375-380 Leupin W, Wagner G, Denny WA, Wiithrich K (1987) Assignment of the carbon-13 nuclear magnetic resonance spectrum of a short DNA-duplex with proton-detected two-dimensional heteronuclear correlation spectroscopy. Nucl Acid Res 15 267-275 Levy GC, Lichter RL (1979) Nitrogen-15 nuclear magnetic resonance spectroscopy. John Wiley, New York... 

One of the most important tasks of modern electrochemistry is to develop microscopic pictures of solid-liquid interfaces and thus to provide a basis for the detailed understanding of electrochemical processes. To fulfill this task, the development of surface-specific and structure-sensitive in-situ methods to characterize electrochemical interfacial processes is indispensable. As early as 1970, Professor Martin Fleischmann was one of the pioneers in exploring in-situ methods that included surface-enhanced Raman spectroscopy [1], surface X-ray diffraction [2] and nuclear magnetic resonance [3] to characterize electrochemical interfaces. Nowadays, nontraditional electrochemical methods that include spectroscopic and microscopic as well as diffraction techniques have been extensively applied, and this has promoted an understanding of electrochemical interfaces at both atomic and molecular levels. 

Because of its high sensitivity, sodium-23 nuclear magnetic resonance (NMR) is useful for the study of ion-substrate interactions(1). Complex formation induces a relaxation enhancement of the nuclear spins manifested by line broadening whereas the position of the peak is little affected. Under sane conditions, such relaxation measurements can be used to determine the forward and the reverse rate constants for conplex formation. In this paper we present exan5)les of the determination of kinetic parameters by NMR. 

The difficulty results, in part, from the fact that only a small fraction of the chemical bonds, generally less than one in a thousand, are involved in me-chanochemical processes. The concentration of connecting units is therefore at the detection limit and below for traditional analytical methods such as conventional nuclear magnetic resonance and infrared spectroscopy. The sensitivity can, of course, be enhanced by techniques such as cumulative, multiple scans, Fourier transform analysis, and difference techniques for detection to one part in ten thousand and better. It may yet be difficult to determine whether polymers are linked by chemical bonds or whether they are simply intimate mixtures. For this distinction, other tests can be of value. For example, the difference between blocks and blends for ethylene-propylene polymer systems has been distinguished by thermal analysis [5]. In many cases, simple extraction tests can distinguish between copolymers and blends. For example, for rubber milled into polystyrene, the fraction of extractable rubber is a measure of mechanochemistry. Conversely, only the rubber in this system is readily cross-linked by benzoyl peroxide after which free polystyrene may be conveniently extracted [6]. In another case, homopolymers of styrene and methyl methacrylate can be separated cleanly from each other and from their copolymers by fractional precipitation [7]. The success of such processes, of course, depends on both the compositions and molecular weights involved. 

T. Mizuno, K. Hioka, K. Fujioka, K. Takegoshi, Development of a magjc-angle spinning nuclear magnetic resonance probe with a cryogenic detection system for sensitivity enhancement, Rev. Sci. Instrum. 79 (4) (2008) 044706. http //dx.doi.Org/10.1063/l. 2912946. 

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