Methods of Sensitivity Enhancement in 13C NMR Spectroscopy

The number of 13C nuclei in the homogeneity range of the magnet can be increased by 13C enrichment of the compound to be measured. Further, the sample concentration at a given volume or the sample volume at a given concentration can be increased the former is limited by limited solubility, the latter by the air gap of the magnet. 

The signal strength increases with the rf power as long as relaxation effects are adequate to restore equilibrium. The method is therefore limited by saturation. 

Accumulation of spectra in a digital computer involving averaging of noise is known as the CAT method (computer averaged transients). The signal noise ratio, S N, increases with the number of accumulated scans n according to eq. (2.1). 

The most economical and efficient method of sensitivity enhancement in 13C NMR of organic molecules is the pulse Fourier transform technique (PFT) in combination with decoupling methods such as proton broad band decoupling and polarization transfer. These methods will be described in the following sections. 

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