NMR systems

The National Chemical Laboratory for Industry (NCLl), Japan, has developed an integrated Spectral Database System (SDBS) which is available to users in Japan. AU spectra were deterrnined at NCLl under controUed conditions and are available on a PC/CD-ROM or magnetic tape. The system has both H-nmr (6000 compounds) and C-nmr spectra (5700 compounds), along with searching software. NCLl has also developed an integrated C— H-nmr system that can be used for two-dimensional data elucidation (70,71). 

Saarinen, TR Woodward, WS, Computer-Controlled Pulsed Magnetic Field Gradient NMR System for Electrophoretic Mobility Measurements, Reviews of Scientific Instruments 59, 761, 1988. 

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. 

Several commercial companies now offer process compatible NMR systems. These systems are either low resolution based on relaxation time measurements or high resolution Fourier Transform spectral measurements. The low resolution systems are manufactured by Process Control Technologies (www.pctnmr.com) and Progression, Inc. (www.progression-systems.com). Progression s systems... 

Fig. 4.7.7 A portable NMR system for measuring freeze damage in Navel oranges. The Halbach magnet is shown above the completed system with two Navel oranges for comparison. The complete system has the battery powered spectrometer electronics housed in a metal box and the system is run by a portable computer.

Of the many areas where NMR is applied these days, two can be considered as being established. The most important is certainly its use for structure elucidation, from small molecules up to medium-sized proteins in solution no university with an analytical lab can afford to be without a liquid-state, high-resolution NMR system. Most chemistry students will come into contact with NMR at least once during their courses. Second, is diagnostic medical imaging, which many of us may have experienced personally. From the first crude and blurred NMR images that were acquired over 30 years ago, incredible developments have been achieved by the efforts of researchers and industry alike. 

MS. Consequently, the layout of Scheme 7.12e has been proposed as an improvement over Scheme 7.12d [671], Some 50-100 p,g of each analyte on the column is needed to obtain identifiable spectra (structure dependent). Sensitivity can be improved to the low p,g or even ng range in miniaturised flow NMR systems. 

In summary, NMR spectroscopy is an extremely versatile tool useful that enables researchers to understand the structure of natural products such as carotenoids. For a full structural assignment, the compound of interest has to be separated from coeluents. Thus, it is a prerequisite to employ tailored stationary phases with high shape selectivity for the separation in the closed-loop on-line LC-NMR system. For the NMR detection, microcoils prove to be advantageous for small quantities of sample. Overall, the closed-loop system of HPLC and NMR detection is very advantageous for the structural elucidation of air- and UV-sensitive carotenoids. 

Systems have been developed by some of the major spectrometer manufacturers to deal specifically with this type of application. These systems are designed with automation very much a priority. Typically, an integrated robot adds a predetermined volume of solvent to each of the wells and then injects the resultant solution into a flow line that transfers it into the spectrometer s probe, which is of course fitted with a flow cell. Spectroscopy can then be performed without the time constraints of the HPLC-NMR system and the sample returned to the well on the plate where it came from, or into a fresh one if required. 

NMR systems are pretty safe if treated correctly but this short chapter outlines some of the things you may need to think about when using them. Note that we are not pretending to offer a full safety assessment but this should alert you to the major hazards associated with modern NMR systems. There are very good documents available from the major NMR manufacturers which cover this area in considerable detail. 

Spend the money wisely - on the best NMR system you can get your hands on - and don t forget to keep your camera handy at next year s office party - you might fancy an upgrade. 

Highly Customized NMR Systems Using an Open-Resource, Home-Built Spectrometer Kazuyuki Takeda... 

In the conventional NMR system used in chemical analyses, downsizing of the spectrometer alone may not be appealing, unless other parts of the system, such as a superconducting magnet, a power amplifier, etc., are also miniaturized. On the other hand, the small-sized spectrometer would find interest in various unconventional scenes. In this section, we show examples of such. 

Figure 13 Snapshots of a portable NMR system serving as a science toy and an education tool. H NMR experiments in water performed (A) at the author s home, and (B and C) in a class room at University of Fukui. A 1 T permanent magnet was used, and the H resonance frequency was 42.6 MHz.

An NMR system using a field-variable, cryogen-free superconducting magnet... 

Figure 15 (A) A desktop NMR system using the OPENCORE NMR spectrometer and a...

Figure 16 shows an NMR system based on the bulk high-temperature superconducting magnet and the OPENCORE NMR spectrometer, in which 1H NMR in water was performed in 4.7 T. 

Figure 16 An NMR system using a bulk high-temperature superconducting magnet and the OPENCORE NMR spectrometer. The temperature of the bulk SCM was 40 K, while the sample space with a diameter of 24 mm was at room temperature. On the computer screen displayed is a hi FID of water taken on this system. The resonance frequency was 200.045 MHz.

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