Nuclear magnetic resonance low-resolution

Low Resolution Nuclear Magnetic Resonance (LR-NMR) systems are routinely used for food quality assurance in laboratory settings [25]. NMR based techniques are standardized and approved by the American Oil Chemist s Society (AOCS) (AOCSd 16b-93, AOCS AK 4-95), the International Union of Pure and Applied Chemistry (IUPAC) (solid fat content, IUPAC Norm 2.150) and the International Standards Organization (ISO) (oil seeds, ISO Dis/10565, ISO CD 10632). In addition to these standardized tests, low resolution NMR is used to measure moisture content, oil content and the state (solid or liquid) of fats in food. Table 4.7.1 summarizes common food products that are analyzed by low-resolution NMR for component concentration. 

Low-resolution nuclear magnetic resonance spectroscopy can also be used to determine percent by weight hydrogen in jet fuel (ASTM D3701) and in light distillate, middle distillate, and gas-oil (ASTM D4808). As noted above, chromatographic methods are not applicable to naphtha, where losses can occur by evaporation. 

Another method (ASTM D-4808) covers the determination of the hydrogen content of petroleum products, including vacuum residua, using a continuous-wave, low-resolution nuclear magnetic resonance spectrometer. Again, sample solubility is a criterion that will not apply to coal but will apply to coal extracts. More recent work has shown that proton magnetic resonance can be applied to solid samples and has opened a new era in coal analysis by this technique (de la Rosa et al., 1993 Jurkiewicz et al 1993). 

ASTM D-4808. Standard Test Methods for Hydrogen Content of Light Distillates, Middle Distillates, Gas Oils, and Residua by Low-Resolution Nuclear Magnetic Resonance Spectroscopy. 

Hinrichs, R., Bulca, S., and Kulozik, U. (2007). Water-mobility during lenneting and acid coagulation of casein solutions a differentiated low-resolution nuclear magnetic resonance (NMR) analysis. Int J. Dairy Technol 60, 37-43. 

The methods used by Canadian plant breeders to determine the oil content of rapeseed may serve as an example of the evolution and adoption of more effective analytical procedures. The methods used for this purpose evolved from the Goldfisch method through the Comstock press method (Comstock and Culbertson, 1958) and the Swedish method (Troeng, 1955) to use of the extremely efficient low resolution nuclear magnetic resonance (NMR) instruments designed to determine oil content. The NMR analyzer permits one technician to perform many times the number of analyses possible with earlier methods. 

This method has the disadvantage of a considerable drying time (usually 4-6 h) and many rapid techniques are now available. Infrared drying ovens and microwave ovens have been shown to produce comparable results to vacuum oven drying methods for various fruit products. Nondestructive techniques such as low-resolution nuclear magnetic resonance... 

International Standard Organization ISO 5511-1992. Oilseeds—Determination of Oil Content—Method using Continuous-Wave Low-Resolution Nuclear Magnetic Resonance Spectrometry (Rapid method). Re-approved in 1997. 

AOCS. Official Method Cd 16b-93, Solid Fat Content (SFC) by Low-Resolution Nuclear Magnetic Resonance—The Direct Method. Champaign, IL Am Oil Chem Soc, 1999. 

A test specimen is compared in a continuous wave, low-resolution nuclear magnetic resonance (NMR) spectrometer with a reference standard sample. The spectrometer... 

Dobrzynski, P., Kasperczyk, J., 2006a. Synthesis of biodegradable copolymers with low-toxicity zirconium compounds. IV. Copolymerization of glycolide with trimethylene carbonate and 2,2-dimethyltrimethylene carbonate microstructure analysis of copolymer chains by high-resolution nuclear magnetic resonance spectroscopy. Journal of Polymer Science Part A Polymer Chemistry 44, 98—114. 

ASTM Test Method D5292, Aromatic Carbon Contents of Hydrocarbon Oils by High Resolution Nuclear Magnetic Resonance Spectroscopy, permits determination of aromatic hydrogen and aromatic carbon content of gas oils, lubricating oils, and other hydrocarbon fractions that are completely soluble in chloroform and carbon tetrachloride at ambient temperatures. Concentrations as low as 0.1 mol-% hydrogen and 0.5 mol-% carbon can be determined. Olefins and phenolic compounds above 1 mass-% interfere. 

Nuclear magnetic resonance traditionally has had low sensitivity and spectral resolution. It can provide rigorous quantification of analytes, but not accurate qualitative identification. Individual resonances may be sensitive to the chemical and physical environment of the molecule, which then requires appropriate preparation of samples. The process also has little dynamic range, in contrast to GC-MS. 

Molecular dynamics (MD) simulations fill a significant niche in the study of chemical structure. While nuclear magnetic resonance (NMR) yields the structure of a molecule in atomic detail, this structure is the time-averaged composite of several conformations. Electronic and vibrational circular dichroism spectroscopy and more general ultraviolet/visible and infrared (IR) spectroscopy yield the secondary structure of the molecule, but at low resolution. MD simulations, on the other hand, yield a large set of individual structures in high detail and can describe the dynamic properties of these structures in solution. Movement and energy details of individual atoms can then be easily obtained from these studies. 

Nuclear magnetic resonance (NMR) can be used as a rapid alternative to differential scanning calorimetry in the determination of the solid fat content and studies on the melting behaviour. The determination is based on detection of the different populations of protons in solid and liquid phases, which indicates the hardness of the fat. Hernandez and Rutledge (1994b) used low resolution pulse NMR to compare melting curves of roasted and non-roasted cocoa butters from Africa, Indonesia and South America. Discriminant analysis techniques showed... 

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