何为"氘锁"？ 以下是引用 lanthanum 在2006-8-25 16:57:00的发言： 请教汪老师： “氘信号锁场”是不是指的用氘代溶剂中残余的氢信号锁场？？ 例如 cdcl3 中的 chcl3 信号在7.26ppm用于锁场？？ 还是指的用氘信号？可是氘信号在哪里呢？仪器方面实在是懂得太少呀。 谢谢汪老师讲解！ field lock in order to produce a high resolution nmr spectrum of a sample, especially one which requires signal averaging or phase cycling, you need to have a temporally constant and spatially homogeneous magnetic field. consistency of the b o field over time will be discussed here; homogeneity will be discussed in the next section of this chapter. the field strength might vary over time due to aging of the magnet, movement of metal objects near the magnet, and temperature fluctuations. here is an example of a one line nmr spectrum of cyclohexane recorded while the b o magnetic field was drifting a very significant amount. the field lock can compensate for these variations. the field lock is a separate nmr spectrometer within your spectrometer. this spectrometer is typically tuned to the deuterium nmr resonance frequency. it constantly monitors the resonance frequency of the deuterium signal and makes minor changes in the b o magnetic field to keep the resonance frequency constant. the deuterium signal comes from the deuterium solvent used to prepare the sample. the animation window contains plots of the deuterium resonance lock frequency, the small additional magnetic field used to correct the lock frequency, and the resultant b o field as a function of time while the magnetic field is drifting. the lock frequency plot displays the frequency without correction. in reality, this frequency would be kept constant by the application of the lock field which offsets the drift. on most nmr spectrometers the deuterium lock serves a second function. it provides the =0 reference. the resonance frequency of the deuterium signal in many lock solvents is well known. therefore the difference in resonance frequency of the lock solvent and tms is also known. as a consequence, tms does not need to be added to the sample to set =0; the spectrometer can use the lock frequency to calculate =0. 查看更多
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