NMR nuclear magnetic resonance spectrometers

Flexible superconducting tapes provide promise of uses for superconductors in motors, generators, and even electric transmission lines. Meanwhile, superconducting magnets cooled to the temperature of liquid helium already are in use. High-field nuclear magnetic resonance (NMR) spectrometers have become standard instruments in chemical research laboratories, and the same type of machine (called an MRI spectrometer) is used for medical diagnosis in hospitals worldwide. 

The final reactant/product mixture was analyzed by a Gemini 300 13C nuclear magnetic resonance (NMR) spectrometer using CDC13 as a solvent. 

Until recently, probably the best understood oxidation state of vanadium was V(IV). This situation changed with the advent of high field nuclear magnetic resonance (NMR) spectrometers, which provided the means to obtain a detailed understanding of the V(V) oxidation state. Indeed, the past 2 decades have seen the redrawing of the landscape of V(V) science, particularly where the aqueous phase is involved. 

The nuclear magnetic resonance (NMR) spectrometer has become in recent years one of the most popular and useful tools available to the chemist for structural studies. In the usual high-resolution NMR spectrum of a liquid the scalar parameter called the chemical shift is readily obtained and may be interpreted in an approximate and qualitative fashion to establish features of the overall structure. The task of placing the interpretation of the chemical shift on a more quantitative and rigorous basis is not an easy one but considerable progress has been made in this direction. The potential rewards of improved understanding in this area seem most attractive. 

These categories include many individual high-cost systems such as nuclear magnetic resonance (NMR) spectrometers. X-ray equipment, and electron microscopy and spectroscopy setups. Sales of spectroscopic instruments that are growing include Fourier transform infrared (FTIR), Raman NMR, plasma emission and energy-dispersive X-ray spectrometers. 

Today the most useful chemical instrument is probably the nuclear magnetic resonance (NMR) spectrometer. Magnetic resonance imaging (MRI), vital in modern medicine, is derived from NMR. In late 1945, a physics group at Stanford, led by Felix Bloch (1905-83) (with William W. Hanson [1909-49] and Martin W. Packard), and one at Harvard, led by Edward M. Purcell (1912-97) (with Henry C. Tbrrey [1911-99] and Robert V. Pound [1919- ]), independently discovered the phenomenon of nuclear magnetic resonance. In order to manifest NMR an atomic nucleus must have nonzero nuclear spin. Of the roughly 100 stable isotopes that have nonzero nuclear spin, H, present in the vast majority of... 

A) Schematic diagram of a simple nuclear magnetic resonance (NMR) spectrometer. The sample is placed in solution in a long, thin tube and spins in a probe sitting in a magnetic and surrounded by radio-frequency (RF) coils B) proton NMR spectrum of ethanol (QH O) with tetramethylsilane (TMS) added as internal standard. On the 8-scale of chemical shifts,... 

NMR Spectrometry If a nuclear magnetic resonance (NMR) spectrometer is available ( 20,000-160,000), the NMR spectrum should be obtained since, of all the spectral methods, this one gives, in general, the most useful information. Infrared and mass spectra contain considerable structural information but much of it is virtually impossible to extract. 

Radiofrequency (RF) radiation occupies the region of approximately 30 kHz to 300 MHz in the electromagnetic spectrum. The most common use of RF is in nuclear magnetic resonance (NMR) spectrometers. 

Some instruments, such as nuclear magnetic resonance (NMR) spectrometers that use superconducting magnets, require cooling by cryogens such as liquid nitrogen and liquid helium. Some freezers use liquid nitrogen to maintain samples at low temperatures. 

Nuclear magnetic resonance (NMR) spectrometers offer spectral capabilities to elucidate polymeric structures. This approach can be used to perform experiments to determine comonomer sequence distributions of polymer products. Furthermore, the NMR can be equipped with pulsed-liied gradient technology (PFG-NMR), which not only allows one to determine self-diffusion coefficients of molecules to better understand complexation mechanisms between a chemical and certain polymers, but also can reduce experimental time for acquiring NMR data. Some NMR instruments can be equipped with a microprobe to be able to detect microgram quantities of samples for analysis. This probe has proven quite useful in GPC/NMR studies on polymers. Examples include both comonomer concentration and sequence distribution for copolymers across their respective molecular-weight distributions and chemical compositions. The GPC interface can also be used on an HPLC, permitting LC-NMR analysis to be performed too. Solid-state accessories also make it possible to study cross-linked polymers by NMR. 

Magnetic Field Strengths of Some Typical Nuclear Magnetic Resonance (NMR) Spectrometers and the Corresponding and NMR Frequencies and CSA (Chemical Shift Anisotropy) Ranges... 

In these experiments, the intensity of absorption at a particular wavelength is measured by a spectrometer appropriate for the visible region of the spectrum. You are not limited to the use of visible-region spectrometers for the determination of reaction rates, however. Depending on the reaction, other types of instruments are used, including infrared (IR) and nuclear magnetic resonance (NMR) spectrometers, which we described briefly in Instrumental Methods essays in earlier chapters. 

Determined by a low angle laser light scattering (LALLS ) device Determined by a H nuclear magnetic resonance (NMR) spectrometer Determined by gel permeation chromatography (GPC) measurement... 

A good pyrolysis instrument must be able to reproducibly, heat a sample to a preset temperature, at a known rate for a specific amount of time. Inability to control any of these variables will result in a pyrogram that cannot be reproduced. If required, the separated pyrolysis products can each be fed into a mass spectrometer to obtain detailed information on pyrolysis product identity (Py-GC-MS) or into a nuclear magnetic resonance (NMR) spectrometer (Py-GG-NMR spectroscopy) or into a Fourier-transform-infrared (FT-IR) spectrometer. 

For the determination of ethylene copolymers containing more than 95 % propylene Paxton and Randall [8] have described a method wherein a 1,2,4 trichlorobenzene -perdeuterobenzene solution of the polymer is examined on a nuclear magnetic resonance (NMR) spectrometer to evaluate methine resonances. The method is calibrated against known copolymers of similar constitution to the copolymers being analysed. 

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

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