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首页> 外文期刊>Journal of magnetic resonance >J-modulation effects in DOSY experiments and their suppression: The Oneshot45 experiment
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J-modulation effects in DOSY experiments and their suppression: The Oneshot45 experiment

机译：DOSY实验中的J调制效应及其抑制：Oneshot45实验

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摘要

Diffusion-ordered spectroscopy (DOSY) is a powerful NMR method for identifying compounds in mixtures. DOSY experiments are very demanding of spectral quality; even small deviations from expected behaviour in NMR signals can cause significant distortions in the diffusion domain. This is a particular problem when signals overlap, so it is very important to be able to acquire clean data with as little overlap as possible. DOSY experiments all suffer to a greater or lesser extent from multiplet phase distortions caused by J-modulation, requiring a trade-off between such distortions and gradient pulse width. Multiplet distortions increase spectral overlap and may cause unexpected and misleading apparent diffusion coefficients in DOSY spectra. These effects are described here and a simple and effective remedy, the addition of a 45° purging pulse immediately before the onset of acquisition to remove the unwanted anti-phase terms, is demonstrated. As well as affording significantly cleaner results, the new method allows much longer diffusion-encoding pulses to be used without problems from J-modulation, and hence greatly increases the range of molecular sizes that can be studied for coupled spin systems. The sensitivity loss is negligible and the added phase cycling is modest. The new method is illustrated for a widely-used general purpose DOSY pulse sequence, Oneshot.
机译：扩散有序光谱法（DOSY）是一种强大的NMR方法，可用于识别混合物中的化合物。 DOSY实验对光谱质量的要求很高。甚至NMR信号中预期行为的微小偏差也会在扩散域中造成明显的失真。当信号重叠时，这是一个特别的问题，因此能够以尽可能少的重叠获取干净的数据非常重要。 DOSY实验都或多或少地受到J调制引起的多重相失真的困扰，这需要在这种失真和梯度脉冲宽度之间进行权衡。多重畸变会增加光谱重叠，并可能导致DOSY光谱出现意料之外的误导性表观扩散系数。本文描述了这些效果，并展示了一种简单有效的补救措施，证明了在采集开始之前立即添加45°冲洗脉冲以消除不需要的反相项。除了提供明显更清洁的结果外，新方法还允许使用更长的扩散编码脉冲，而不会受到J调制的影响，因此大大增加了可用于耦合自旋系统的分子大小范围。灵敏度损失可以忽略不计，而且增加的相位循环也很适中。针对广泛使用的通用DOSY脉冲序列Oneshot说明了该新方法。

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