Signal Enhancement Via The INEPT Technique
The INEPT signal enhancement has two sources:
- The spin population effect increases the signal by a factor of K = ratio of gyromagnetic ratios γI/γS of the nuclei, where γI and γS are the gyromagnetic ratio of the proton (the I spins) and the low-sensitivity nuclei (the S spins) respectively.
- Nuclei with higher magnetogyric ratio generally relax more quickly. Since the rate at which the INEPT transfer can be repeated is limited by the relaxation of these spins (rather than the low sensitivity spins), then the experiment can be repeated more frequently, increasing the signal-to-noise ratio.
As a result, INEPT can enhance the NMR signal by a factor larger than K, while the maximum enhancement via NOE is by a factor of 1+K/2. Unlike NOE, in INEPT, no penalty is incurred by a negative gyromagnetic ratio, it is therefore a useful method for enhancing the signal from nuclei with negative gyromagnetic ratio such as 15N or 29Si. The 15N signal may be enhanced by a factor of 10 via INEPT.
Read more about this topic: Insensitive Nuclei Enhanced By Polarization Transfer
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