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So a solid state spectrum is analogous to a liquid state spectrum.  However, notice that the signals are much broader than those of a liquid state spectrum and interpretation is much more difficult.   Solid state NMR is not the method of choice for identifying unknown materials or structure elucidation.  

We have to overcome three obstacles in taking an NMR spectrum of a solid, dipolar coupling, chemical shift anisotropy.

  Dipolar Coupling- When a solid is exposed to the magnetic field, the magnetic nuclei in this case 1H, will be polarized with or against the field.   These nuclei generate magnetic fields of their own and cause additions and subtractions in field strength to the nuclei we observe, 13C.  These additions and subtractions are dependent on distance and alignment and vary greatly from one nucleus to another, thus causing a broadening of the NMR signal on the order of several KHz.  This would be a huge problem.

Chemical Shift Anisotropy-   The chemical shift of any given 13C nucleus depends on its position it the matrix, and every position will experience a different magnetic field.   This is due to the secondary fields generated by the various atomic arrangements. 

 The problems of low sensitiviy and dipolar coupling are overcome by the cross polarization sequnece.   In the figure below time progreses from left to right.

Cross polarization sequence

The 1H channel is above and the 13C below. The first step is a 900  1H  pulse.  Immediately afterwards rf radiation is applied to both channels at precise power levels so that the precession frequencies of the 1H and 13C nuclei become equal, the Hartman Hahn match.  When this condition is achieved the much more abundant 1H polarization is transfered to the 13C nuclei resulting in a large increase in 13C signal strength.  After this cross polarization step, the 13C signal is acquired with high power 1H decoupling.   Very high power 1H decoupling is needed to overcome the dipoar coupling.

 

 

 

Solids probe  RotorCSA is overcome by magic angle spinning.  The sample is placed in a ceramic rotor capped with a small turbine.  The rotor is placed in probe at an angle of 540 with the magnetic field and spun at a rate of 2 to 6 kHz. 

On the far left is a picture of a solid state probe with the shield removed.  Notice how the stator is tilted 540.  To the left of the picture is the tygon tube that suppies the spinner air and the black fiber optic cable for the tachometer. 

To the immediate left is a picture of two rotors with turbines.