Sample preparation magnetic field homogeneity

Sample Preparation. As mentioned above, very high purity is not normally essential, but certain types of impurities such as paramagnetic substances must be excluded. The presence of solid impurities of any sort in the solution of a substance will degrade the homogeneity of the magnetic field and hence cause line broadening. For this reason solutions should be filtered before being placed in the NMR sample tube. 

During sample preparation for NMR spectroscopy, the sample tubes should be clean and free of any contaminants. The sample should be dry and free of any solvent. The NMR samples are prepared by dissolving the sample in a solvent containing deuterium. The most common solvent is deuterated chloroform. The sample should be completely dissolved in the solvent because undissolved particles can distort the homogeneity of the magnetic field. 

A number of methods have been used in the synthesis of perovskites the choice of a particular one depends mostly on the expected use for these oxides. Obviously, no attention has been paid to textural characteristics of samples whose uses are based on their electric or magnetic properties. However, application of perovskites in the field of catalysis requires solids with a well-developed porous network. As the present review is concerned particularly with the surface and catalytic properties of perovskites, we will place special emphasis on preparation methods leading to a high surface volume ratio. Also, methods yielding homogeneous solids will be discussed because of the important effect that inhomogeneities may play in heterogeneous catalysis. 

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