Spectrometer magnetic resonance

The speed with which NMR spectroscopy has been incorporated into scientific inquiry is truly amazing. The first commercial spectrometers became available in the 1950s. By the middle 1980s whole bodies could be placed in the probes of NMR spectrometers (magnetic resonance imaging) and the structures of body parts could be determined in exquisite detail. Today structures of proteins and other macromolecules in solution or in the solid state are determined routinely. What was unthinkable in the 1960s is routinely practiced today even by undergraduates The power of the method and the structural detail it provides have no doubt fueled its rapid development. 

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... 

The chapter is divided into sections, one for each general class of mass spectrometer magnetic sector, quadnipole, time-of-flight and ion cyclotron resonance. The experiments perfonned by each are quite often unique and so have been discussed separately under each heading. 

FIGURE 13 5 Diagram of a nuclear magnetic resonance spectrometer (Reprinted with permis Sion from S H Pine J B Hendrickson D J Cram and G S Hammond Organic Chemistry 4th ed McGraw Hill New York 1980 p 136)... 

Nuclear Magnetic Resonance. In 1994 there were three principal vendors of nmr instmmentation in the U.S., Bmker Instmments (Billerica, Mass.), JEOL USA, Inc. (Peabody, Mass.), and Varian Associates (Palo Alto, Calif.). Details of instmmentation are best obtained directly from manufacturers. A schematic illustrating the principal components of a ft/nmr spectrometer is shown in Eigure 3. 

Fig. 3. A block diagram schematic representation of a Fourier transform nmr spectrometer, ie, a superconducting magnetic resonance system.

Proton nuclear magnetic resonance spectra of 15-20% solutions of polymers in CC14 were obtained with Varian T-60 or HR-300 spectrometers. Chemical shifts are reported... 

Magnetic resonance imaging is a noninvasive structural technique for complex systems of molecules, such as people. In its simplest form, MRI portrays the concentration of protons in a sample. If the sample—which may be a living human body—is exposed to a uniform magnetic field in an NMR spectrometer and if we work at a resolution that does not show any chemical shifts or fine structure, then the protons... 

A solid-state nuclear magnetic resonance (NMR) experiment was carried out in 4 mm double bearing rotor made from Zr02 on a Bruker DSX 200 MHz spectrometer with resonance frequency at 75.468 MHz. The pulse length was 3.5 ps and the contact time of IH-13C CP was 2-5 ms. 

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. 

Fourier transform infrared (FTIR) spectroscopy was performed oj a Nicolet 10DX spectrometer. Nuclear magnetic resonance ( H) characterization was accomplished using an IBM 270 SL. Both techniques can successfully be utilized to analyze both the diblock precursors as well as the derived acid containing polymers. 

Proton and carbon-13 nuclear magnetic resonance (NMR) spectra were recorded on a IBM Instruments 270 MHz NMR Spectrometer on 6-8 weight percent solutions in deuterated chloroform. Ultraviolet spectra were recorded on an IBM Ultraviolet Spectropluitometer Model 9420 using chloroform solutions containing 2 x 10-5 g/ml of the copolymers. 

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

If one wishes to obtain a fluorine NMR spectrum, one must of course first have access to a spectrometer with a probe that will allow observation of fluorine nuclei. Fortunately, most modern high field NMR spectrometers that are available in industrial and academic research laboratories today have this capability. Probably the most common NMR spectrometers in use today for taking routine NMR spectra are 300 MHz instruments, which measure proton spectra at 300 MHz, carbon spectra at 75.5 MHz and fluorine spectra at 282 MHz. Before obtaining and attempting to interpret fluorine NMR spectra, it would be advisable to become familiar with some of the fundamental concepts related to fluorine chemical shifts and spin-spin coupling constants that are presented in this book. There is also a very nice introduction to fluorine NMR by W. S. and M. L. Brey in the Encyclopedia of Nuclear Magnetic Resonance.1... 

To evaluate set-up costs we assume that we have to start from scratch. From our previous discussion about microwave frequencies it should be obvious that we want a cw X-band spectrometer as the central (frequently only) facility. What exactly is a complete spectrometer The answer depends a bit on the type of experiments planned, but for all cases the minimum requirements would be a basic spectrometer (bridge + resonator magnet control unit) and a frequency counter. 

The basic instrumentation used for spectrometric measurements has already been described in Chapter 7 (p. 277). The natures of sources, monochromators, detectors, and sample cells required for molecular absorption techniques are summarized in Table 9.1. The principal difference between instrumentation for atomic emission and molecular absorption spectrometry is in the need for a separate source of radiation for the latter. In the infrared, visible and ultraviolet regions, white sources are used, i.e. the energy or frequency range of the source covers most or all of the relevant portion of the spectrum. In contrast, nuclear magnetic resonance spectrometers employ a narrow waveband radio-frequency transmitter, a tuned detector and no monochromator. 

The nuclear magnetic resonance spectrum of sodium valproate as shown in Figure 3 was obtained on a Varian Associates T-60 NMR Spectrometer in deuterium oxide containing tetramethylsilane as the internal standard. The spectral peak assignments (2) are presented in Table I. 

The polarization patterns are dependent upon the strength of the magnetic field, in which the reactions are carried out. If the reactions are carried out at high fields (i.e., notably within the NMR spectrometer), the resonances appear in antiphase - that is, there is an equal number of absorption and emission lines and no net polarization. At low field however (i.e., when the reaction is carried out at zero or a very low field and then transferred into the high field of the NMR spectrometer for subsequent investigation), the resonances display net polarization, as has been outlined by Pravica and Weitekamp [9]. 

Infrared (IR) spectra were measured on a Beckmann Microlab 600 model spectrophotometer. Nuclear magnetic resonance (NMR) spectra were measured on a Varian EM360 spectrometer, with 19F-spectra collected using trifluoroacetic acid as a standard, or with H-spectra collected using tetramethylsilane as a standard. 

Fourier transform nuclear magnetic resonance (nmr), 21 278 Fourier transform spectrometers, 19 671 23 137... 

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