NMR研究样品处理的有用技巧

In comparison with handling of samples for other spectroscopic techniques samples for NMR analysis require special care. Failure to adhere to recommended practices can result in gross errors or even accidents. In the present article some guidelines are suggested to help avoid such situations.

Sample Size

Sample size of 1-10mg is sufficient for proton NMR of an organic compound in a short time span of around 10-15 minutes. Larger quantities (5-50mg) are needed for low sensitivity 13C NMR measurements and field exposure time requirement is also longer (5-30minutes). Larger molecules such as polymeric materials can require sample sizes even above 50mg and still longer observation times.

悬浮固体颗粒

Suspended solids in a solution disturb the magnetic field homogeneity resulting in band broadening. All solutions should be filtered using appropriate filters to remove any suspended solids before introduction into NMR tubes.

样品数量

The NMR tube should be filled to an appropriate depth of 4.5-5.0cm. A scale can be used for the purpose but if a mark is made on the tube for consistent filling it should be cleaned with an appropriate solvent and dried before insertion into the sample tube cavity.

垫片线圈正确地扭曲了磁场中的扭曲。低样本深度可能需要增加光滑时间，而过多的填充可能会增加额外昂贵的剥离溶剂成本。

Tube Cleanliness

The NMR tube should be clean from both inside and outside. Solid particles sticking to outside walls can disturb magnetic field homogeneity. Routinely the tube should be washed with water, followed with acetone and dried. It should be cleaned with glass wool. A brush should not be used for cleaning as it can erode the tube leading to impairment of spectral resolution. Tube cap contamination of sample cannot be ignored. It is advisable to cover the top with a Teflon tape and then cap it. Never invert the tube for mixing but instead use a vortex mixer.

试管标签

切勿沿着管长度写样本细节。建议将贴纸或胶带标签包裹在管子的顶端，或者如果将胶带固定在盖上，则可以更好。由于管子在磁铁腔内以高速旋转时，不应将襟翼或悬空的松散标签固定在管子上。

Sample Degassing

Oxygen in the air has paramagnetic properties and any air dissolved in the sample should be removed by degassing for analysis requiring high sensitivity. The sample should be prepared in an inert environment and run at the earliest after preparation.

Solvent Choice

建议先在普​​通的质子溶剂中测试样品溶解度，然后采用相应的氘化溶剂，以节省更高的氘化溶剂成本。大多数溶剂本质上都是有毒的，因此您需要熟悉它们的安全方面，然后才能处理样品准备。

It goes without saying that full care and precautionary measures need to be adopted in sample preparation to ensure consistent sensitivity and safety of operations.