Small-scale NMR Reaction Monitoring

The factor Bi/i in Eq. (2.5.6), the magnetic field per unit current, is defined to be the coil sensitivity. For almost all coil geometries, the value of Bi/i is inversely 

The development of microcoil techniques has been reviewed by Minard and Wind [24, 25] and by Webb [26]. In a more recent publication Seeber et al. reported the design and testing of solenoidal microcoils with dimensions of tens to hundreds of microns [27]. For the smallest receiver coils these workers achieved a sensitivity that was sufficient to observe proton NMR with an SNR of unity in a single scan of 10 pm3 (10 fL) of water, containing 7 x 1011 proton spins. Reducing the diameter of the coil from millimeters to hundreds of microns thus increases its sensitivity greatly, allowing analysis of pL to pL sample volumes. 

Although one can potentially attempt to cool the rf microcoil, which according to Eq. (2.5.2) would further improve the SNR by reducing the Rcoii term in the denominator, in the case of microcoils the sample is extremely close to the coil and if the sample has to be kept at room temperature, cooling the coil alone is extremely difficult. 

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