步进累加方法的实践

本文由理论与实验证明步进累加方法本质上是一种狭带的带通滤波的选择接收方法。其线型为类sinc函数。累加的结果与累加次数有关。对单脉冲后步进累加在一定次数以后即趋近饱和。对类回波的接收则出现极大值。只有在弱耦合体系中且offset选择在化学位移处才能得到所谓化学位移滤波。最后讨论实验条件及应用例子。

THE PRACTICE OF STEP-PROGRESSIVE ACCUMULATION IN NMR

It is proved by theory and experiments in this paper that (a) the results of step-progressive accumulation (SPA) is essentially a narrow band -pass filter. The line -shape is a like -sinc function. In the single pulse case, the amplitude of the selected peak will approach to a maximum value with the increment of the accumulation number N. For two pulses case, the maximum amplitude appears only in the optimum N, which depends on the step-length of SPA. (b) The realization of so-called chemical shifts filter (CSF) depends on the offset used in experiment and the coupling of spin system. For weakly coupling spin system, CSF can be observed only if the offset is put on the chemical shift of this system. When the offset is set on one peak of the spectrum, only this peak will be observed. For the strong coupling spin system, CSF is no longer valid. At last, the choice of parameters in SPA experiments and some applications are discussed.