A new water suppression technique for generating pure-phase spectra with equal excitation over a wide bandwidth
A new water suppression technique for generating pure-phase spectra with equal excitation over a wide bandwidth
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一种新的水抑制技术，可在宽带宽上产生等激励的纯相光谱
DOI：
10.1016/0022-2364(87)90046-1
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发表时间：
1987
影响因子：
2.2
通讯作者：
A. Bax
中科院分区：
文献类型：
--
作者：
V. Sklenar;A. Bax
最近已经提出了大量新的选择性激发方法用于抑制溶解在H2O中的样品的NMR光谱的Hz 0共振。这些方法包括分时硬脉冲序列（1 -4）、硬脉冲和软脉冲的组合（5，6）和“两级”分时硬脉冲序列（7，8）。在两级抑制中，每个单独扫描的抑制相对较低，但足以避免光谱仪接收器中的动态范围问题;在第二级（由11个重聚焦脉冲的EXORCYCLE（9）相位循环组成）之后，可以获得非常高的抑制。上面提到的所有方法以及之前提出的大量其他方案都非常适合于生成常规的1D NMR谱。用这些方法中的大多数获得的1D NMR谱中的相位失真可以通过线性或更高阶相位校正在很大程度上去除，并且剩余的基线失真通常不妨碍峰位置或强度的准确测量。然而，当生成相敏2D NMR谱时，在第一傅立叶变换之后剩余的基线失真在最终2D谱中引起严重失真，特别是在强共振附近。即使相对较小的相位失真（4，5）也会导致2D频谱中的严重基线问题。只有少数几种方法可以产生没有任何相位失真的光谱。这些包括（a）90 "-902“（I-1或跳跃返回）序列（1）（B）一个软（高斯）形90”脉冲，后面跟着一个非选择性902脉冲（5）和（c）“11回波”方案（7）。方案（a）和（B）由于激励分布中的尖锐零点而提供了对HZ 0谐振的相对差的抑制;方案（c）提供了高抑制，但具有激励分布的不期望的sin 3偏移依赖性。在这里，我们提出了一种新的方法，两阶段的类型，提供了非常好的水抑制和一个近乎理想的激励配置文件。脉冲方案在图la中描绘。该序列以软900脉冲开始，该脉冲将HZ 0磁化旋转到旋转框架的x轴。随后的非选择性90 °脉冲，随后是一个短的（约2毫秒）自旋锁被用来测量剩余的z磁化。水的抑制可从一个单一的前-
A large variety of new selective excitation methods recently has been proposed for suppressing the Hz0 resonance from the NMR spectra of samples dissolved in H20. These methods include time-shared hard pulse sequences (l-4), combinations of hard and soft pulses (5, 6) and “two-stage” time-shared hard pulse sequences (7, 8). In the two-stage suppression, the suppression per individual scan is relatively low but sufficient to avoid dynamic range problems in the spectrometer receiver; after the second stage (consisting of EXORCYCLE (9) phase cycling of a ll refocusing pulse) very high suppression can be obtained. All approaches mentioned above, as well as a large number of other schemes proposed previously, are well suited for generating conventional 1 D NMR spectra. Phase distortions in the 1 D NMR spectra obtained with most of these methods can be removed to a large extent by linear or higher order phase corrections, and the remaining baseline distortions generally do not prohibit accurate measurement of peak positions or intensities. However, when generating phase-sensitive 2D NMR spectra, baseline distortions remaining after the first Fourier transformation give rise to serious distortions in the final 2D spectrum, especially in the vicinity of intense resonances. Even relatively small phase distortions (4, 5) can cause severe baseline problems in the 2D spectrum. Only a few methods are available that yield spectra without any phase distortion. These include (a) the 90,“-902,(I-1 or jumpand-return) sequence (1)(b) a soft (Gaussian)-shaped 90,” pulse followed by a nonselective 902, pulse (5) and (c) the “ll echo” scheme (7). Schemes (a) and (b) provide relatively poor suppression of the HZ0 resonance due to the sharp null in the excitation profile; scheme (c) provides high suppression but has an undesirable sin3 offset dependence of the excitation profile. Here we present a new method, of the twostage type, that offers very good water suppression and a nearly ideal excitation profile. The pulse scheme is depicted in Fig. la. The sequence starts with a soft 900, pulse that rotates the HZ0 magnetization to the x axis of the rotating frame. A subsequent nonselective 90, pulse followed by a short (about 2 ms) spin lock is used to measure the remaining z magnetization. The water suppression obtainable from a single ex-