Dedicated NMR

Here Tz enters as the limit of Tip for vanishing lock-field strength Buy. Therefore, given a Ti parameter image and a map of B y R), the correlation time Xc of molecular motion can be mapped in the weak collision limit. 

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The first of these could well be research chemists and students in an academic or industrial environment who need to know what modern techniques are available to assist them in their efforts, but otherwise feel they have little concern for the operation of a spectrometer. Their data is likely to be collected under fully automated conditions or provided by a central analytical facility. The second may be a chemist in an academic environment who has hands-on access to a spectrometer and has his or her own samples that demand specific studies that are perhaps not available from fully automated instrumentation. The third class of reader may work in a smaller chemical company or academic chemistry department who have invested in NMR instrumentation but may not employ a dedicated NMR spectroscopist for its upkeep, depending instead on, say, an analytical or synthetic chemist for this. This, it appears (in the UK at least), is often the case for new... 

In general, these modified probes give more accurate data on real catalysis as they are not closed systems, and constant partial pressures of reactive gases can be maintained. However, they are not so easy to use, require a wide bore magnet, and also usually a dedicated NMR. 

However, NMR has the potential of being very useful in process analysis due to it being a noncontact and nondestructive technique. Another problem that was faced when NMR was initially tried as an online application was that laboratory instruments were simply moved into the plant. Process operators found problems in the calibration and maintenance of these instruments. Recently, small, dedicated NMR systems have been developed, which in turn has led to more reports of online NMR. Time domain measurements (low field, low resolution) are far more... 

A block diagram of a typical instrumental set-up for HPLC-NMR is shown in Figure 1. This comprises a high-resolution NMR spectrometer with its superconducting magnet into which is placed a dedicated NMR flow probe, a standard HPLC system controlled by PC-resident software and a flow control unit which enables the system to be operated in four main modes as listed below. 

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