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小木虫论坛-学术科研互动平台 » 化学化工区 » 催化 » 表征 » 【讨论】MAS NMR什麽含义
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tianwei1332

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[交流] 【讨论】MAS NMR什麽含义已有7人参与

MAS NMR什麽含义？是不是固态核磁共振？能给出什麽信息？
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1楼2010-06-02 17:13:57
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nmrservice

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我这边有专业的宽腔固体核磁共振波谱仪，可以做魔角旋转固体核磁共振，欢迎联系nmrservice@163.com

[ Last edited by nmrservice on 2010-6-7 at 10:08 ]
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7楼2010-06-07 10:07:38
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liconglin970410(金币+1):多谢交流，欢迎常来 2010-06-08 14:26:53
固体样品放在特殊的样品管内旋转，旋转轴与磁场轴线成一特定的夹角（称为魔角，为54。73度）。MAS= Magic Angle Spin. 样品量根据样品管的大小而定，一般不超过1克。
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2楼2010-06-02 17:18:36
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aust_jhe

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liconglin970410(金币+3):多谢，欢迎常来交流 2010-06-08 14:27:17
MAS NMR Magic Angle Spinning Nuclear Magnetic Resonance
In nuclear magnetic resonance, magic angle spinning (MAS) is a technique often used to perform experiments in solid-state NMR spectroscopy.

By spinning the sample (usually at a frequency of 1 to 70 kHz) at the magic angle θm (ca. 54.74°, where cos2θm=1/3) with respect to the direction of the magnetic field, the normally broad lines become narrower, increasing the resolution for better identification and analysis of the spectrum.

In any condensed phase, a nuclear spin experiences a great number of interactions. The main three interactions (dipolar, chemical shift anisotropy, quadrupolar) often lead to very broad and featureless lines. However, these three interactions in solids are time-dependent and can be averaged by MAS. The nuclear dipole-dipole interaction, between magnetic moments of nuclei averages to zero only at the magic angle, θm . The chemical shift anisotropy, a nuclear-electron interaction, averages to a non-zero value. The quadrupolar interaction is only partially averaged by MAS leaving a residual secondary quadrupolar interaction. In liquids, e.g. a solution of an organic compound, most of these interactions will average out because of the rapid time-averaged molecular motion that occurs. This orientation averaging in solution is mimicked by MAS of a solid. This causes the signal to become much narrower, giving rise to the isotropic value (which is of interest for structural determination of solid materials and compounds) and spinning sidebands which occur at multiples of the spinning speed and can be used to determine the chemical shift anisotropy of the nuclei.

The physical spinning of the sample is achieved via an air turbine mechanism. These turbines (or rotors) come in a variety of diameters (outside diameter), from 2.0-15.0 mm, and are usually spun on air or nitrogen gas. The rotors are made from a number of different materials such as ceramics e.g. zirconia, silicon nitride or polymers such as poly-methyl-methacrylate (PMMA), polyoxymethylene (POM). The cylindrical rotors are axially symmetric about the axis of rotation. Samples are packed into the rotors and these are then sealed with a single or double end cap. These caps are made from number of different materials e.g. Kel-F, Vespel, zirconia or boron nitride depending on the application required.
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天天学习，好好向上
4楼2010-06-02 18:51:43
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jungxb

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"固体样品放在特殊的样品管内旋转，旋转轴与磁场轴线成一特定的夹角（称为魔角，为54。73度）。MAS= Magic Angle Spin. 样品量根据样品管的大小而定，一般不超过1克。"

二楼说的对,主要是用于实时检测化合物中的NMR谱图变化情况,通过不同时间化合物峰形及化学位移的变化来判断样品管中物质的变化过程.

做起来好象很贵,而且可以做的单位也很少.
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5楼2010-06-02 21:39:51
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