| SETTING UP YOUR EXPERIMENT | ||||||
| Designing an NMR experiment: | ||||||
| Pulse-sequence diagrams. | ||||||
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From the previous discussions, it should be clear that many parameters must be accounted for in the design of an NMR experiment, even for a very simple run. One powerful way of displaying this information graphically is the pulse-sequence diagram, such as the one shown below. The green pulse shown at left is labeled with its width (p/2 radians = 90o) and phase (the axis along which the pulse is applied). The time period t1 is the acquisition (or detection) period, and t2 is the pulse delay. Control of the acquisition time will be discussed in an upcoming section. At the time indicated by the dotted line, the receiver stops recording signal and the system simply waits for t2, during which the magnetization returns to equilbrium.Move your mouse over the pulse diagram to see the interval during which the signal is detected. |
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| This diagram provides a spectroscopist with enough information to allow her or him to program the spectrometer with the appropriate timing parameters, although this doesn't need to be done very often, since a wide variety of standard sequences is included with all modern instruments. Appropriate values of the pulse width, t1, and t2 are simply entered into the operating software. | ||||||
| If a second pulse is added to the sequence, another time interval (t3) is introduced, as shown below. The data is still acquired during t1, as can be seen when the mouse is positioned over the image: | ||||||
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| The pulse sequences given above are among the simplest used for NMR spectroscopy. The first can be used to acquire a one-dimensional 1H spectrum; the second, to measure T1. However, such diagrams can easily be extended to describe quite complex pulse sequences. | ||||||
